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	$26.95	4.451%	$28.1495	$28.15	$28.15	$28.10
Purchase #2	$235.45	9.309%	$257.368	$257.37	$257.35	$257.40
Purchase #3	$40.41	6.204%	$42.917	$42.92	$42.90	$42.90
Purchase #4	$57.67	8.408%	$62.5189	$62.52	$62.50	$62.50
Purchase #5	$52.89	6.796%	$56.4844	$56.48	$56.50	$56.50
Purchase #6	$179.36	4.607%	$187.6231	$187.62	$187.60	$187.60
Purchase #7	$140.51	9.144%	$153.3582	$153.36	$153.35	$153.40
7 purchase totals =	$733.24		$788.4191	$788.42	$788.35	$788.40