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	$86.60	8.449%	$93.9168	$93.92	$93.90	$93.90
Purchase #2	$120.32	6.300%	$127.9002	$127.90	$127.90	$127.90
Purchase #3	$203.59	9.325%	$222.5748	$222.57	$222.55	$222.60
Purchase #4	$40.43	10.340%	$44.6105	$44.61	$44.60	$44.60
Purchase #5	$197.60	11.180%	$219.6917	$219.69	$219.70	$219.70
Purchase #6	$26.87	3.481%	$27.8053	$27.81	$27.80	$27.80
Purchase #7	$210.60	11.768%	$235.3834	$235.38	$235.40	$235.40
7 purchase totals =	$886.01		$971.8827	$971.88	$971.85	$971.90