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	$183.33	13.529%	$208.1327	$208.13	$208.15	$208.10
Purchase #2	$154.94	10.316%	$170.9236	$170.92	$170.90	$170.90
Purchase #3	$221.30	12.785%	$249.5932	$249.59	$249.60	$249.60
Purchase #4	$142.33	8.300%	$154.1434	$154.14	$154.15	$154.10
Purchase #5	$65.50	9.495%	$71.7192	$71.72	$71.70	$71.70
Purchase #6	$197.39	6.143%	$209.5157	$209.52	$209.50	$209.50
Purchase #7	$50.64	6.483%	$53.923	$53.92	$53.90	$53.90
7 purchase totals =	$1,015.43		$1,117.9508	$1,117.94	$1,117.90	$1,117.80