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	$85.87	5.791%	$90.8427	$90.84	$90.85	$90.80
Purchase #2	$131.34	12.614%	$147.9072	$147.91	$147.90	$147.90
Purchase #3	$208.94	9.573%	$228.9418	$228.94	$228.95	$228.90
Purchase #4	$190.39	10.854%	$211.0549	$211.05	$211.05	$211.10
Purchase #5	$173.74	5.449%	$183.2071	$183.21	$183.20	$183.20
Purchase #6	$243.68	8.130%	$263.4912	$263.49	$263.50	$263.50
Purchase #7	$80.70	11.717%	$90.1556	$90.16	$90.15	$90.20
7 purchase totals =	$1,114.66		$1,215.6005	$1,215.60	$1,215.60	$1,215.60