Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$28.31	11.102%	$31.453	$31.45	$31.45	$31.50
Purchase #2	$147.55	10.393%	$162.8849	$162.88	$162.90	$162.90
Purchase #3	$19.71	4.644%	$20.6253	$20.63	$20.65	$20.60
Purchase #4	$223.43	5.324%	$235.3254	$235.33	$235.35	$235.30
Purchase #5	$18.44	3.585%	$19.1011	$19.10	$19.10	$19.10
Purchase #6	$154.59	5.216%	$162.6534	$162.65	$162.65	$162.70
Purchase #7	$213.68	11.630%	$238.531	$238.53	$238.55	$238.50
7 purchase totals =	$805.71		$870.5741	$870.57	$870.65	$870.60