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	$209.48	3.808%	$217.457	$217.46	$217.45	$217.50
Purchase #2	$142.79	12.208%	$160.2218	$160.22	$160.20	$160.20
Purchase #3	$142.70	9.417%	$156.1381	$156.14	$156.15	$156.10
Purchase #4	$151.70	5.234%	$159.64	$159.64	$159.65	$159.60
Purchase #5	$126.82	11.330%	$141.1887	$141.19	$141.20	$141.20
Purchase #6	$64.37	12.565%	$72.4581	$72.46	$72.45	$72.50
Purchase #7	$56.29	9.530%	$61.6544	$61.65	$61.65	$61.70
7 purchase totals =	$894.15		$968.7581	$968.76	$968.75	$968.80