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	$53.95	8.240%	$58.3955	$58.40	$58.40	$58.40
Purchase #2	$84.61	6.518%	$90.1249	$90.12	$90.10	$90.10
Purchase #3	$137.67	7.262%	$147.6676	$147.67	$147.65	$147.70
Purchase #4	$98.55	8.614%	$107.0391	$107.04	$107.05	$107.00
Purchase #5	$40.61	12.566%	$45.7131	$45.71	$45.70	$45.70
Purchase #6	$91.66	8.354%	$99.3173	$99.32	$99.30	$99.30
Purchase #7	$88.55	13.401%	$100.4166	$100.42	$100.40	$100.40
7 purchase totals =	$595.60		$648.6741	$648.68	$648.60	$648.60