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	$212.93	10.853%	$236.0393	$236.04	$236.05	$236.00
Purchase #2	$72.82	13.573%	$82.7039	$82.70	$82.70	$82.70
Purchase #3	$243.50	13.803%	$277.1103	$277.11	$277.10	$277.10
Purchase #4	$74.59	10.265%	$82.2467	$82.25	$82.25	$82.20
Purchase #5	$88.57	4.670%	$92.7062	$92.71	$92.70	$92.70
Purchase #6	$100.46	3.364%	$103.8395	$103.84	$103.85	$103.80
Purchase #7	$50.83	12.467%	$57.167	$57.17	$57.15	$57.20
7 purchase totals =	$843.70		$931.8129	$931.82	$931.80	$931.70