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	$30.36	6.617%	$32.3689	$32.37	$32.35	$32.40
Purchase #2	$198.83	13.344%	$225.3619	$225.36	$225.35	$225.40
Purchase #3	$133.79	9.229%	$146.1375	$146.14	$146.15	$146.10
Purchase #4	$134.33	10.666%	$148.6576	$148.66	$148.65	$148.70
Purchase #5	$214.95	5.828%	$227.4773	$227.48	$227.50	$227.50
Purchase #6	$53.51	10.691%	$59.2308	$59.23	$59.25	$59.20
Purchase #7	$202.59	4.869%	$212.4541	$212.45	$212.45	$212.50
7 purchase totals =	$968.36		$1,051.6881	$1,051.69	$1,051.70	$1,051.80