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	$155.95	8.167%	$168.6864	$168.69	$168.70	$168.70
Purchase #2	$246.32	13.629%	$279.891	$279.89	$279.90	$279.90
Purchase #3	$56.39	6.263%	$59.9217	$59.92	$59.90	$59.90
Purchase #4	$80.80	9.613%	$88.5673	$88.57	$88.55	$88.60
Purchase #5	$231.33	6.285%	$245.8691	$245.87	$245.85	$245.90
Purchase #6	$36.92	11.197%	$41.0539	$41.05	$41.05	$41.10
Purchase #7	$87.43	10.770%	$96.8462	$96.85	$96.85	$96.80
7 purchase totals =	$895.14		$980.8356	$980.84	$980.80	$980.90