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	$111.93	7.341%	$120.1468	$120.15	$120.15	$120.10
Purchase #2	$71.31	6.425%	$75.8917	$75.89	$75.90	$75.90
Purchase #3	$72.27	6.635%	$77.0651	$77.07	$77.05	$77.10
Purchase #4	$87.98	10.276%	$97.0208	$97.02	$97.00	$97.00
Purchase #5	$77.45	6.227%	$82.2728	$82.27	$82.25	$82.30
Purchase #6	$171.91	10.250%	$189.5308	$189.53	$189.55	$189.50
Purchase #7	$61.31	10.329%	$67.6427	$67.64	$67.65	$67.60
7 purchase totals =	$654.16		$709.5707	$709.57	$709.55	$709.50