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	$88.32	13.352%	$100.1125	$100.11	$100.10	$100.10
Purchase #2	$208.45	8.182%	$225.5054	$225.51	$225.50	$225.50
Purchase #3	$191.26	6.515%	$203.7206	$203.72	$203.70	$203.70
Purchase #4	$58.85	11.852%	$65.8249	$65.82	$65.80	$65.80
Purchase #5	$220.98	12.434%	$248.4567	$248.46	$248.45	$248.50
Purchase #6	$99.25	13.438%	$112.5872	$112.59	$112.60	$112.60
Purchase #7	$160.69	9.286%	$175.6117	$175.61	$175.60	$175.60
7 purchase totals =	$1,027.80		$1,131.8190	$1,131.82	$1,131.75	$1,131.80