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	$75.25	13.248%	$85.2191	$85.22	$85.20	$85.20
Purchase #2	$58.73	6.383%	$62.4787	$62.48	$62.50	$62.50
Purchase #3	$21.88	12.406%	$24.5944	$24.59	$24.60	$24.60
Purchase #4	$126.35	8.744%	$137.398	$137.40	$137.40	$137.40
Purchase #5	$53.85	10.845%	$59.69	$59.69	$59.70	$59.70
Purchase #6	$236.60	11.668%	$264.2065	$264.21	$264.20	$264.20
Purchase #7	$151.30	13.792%	$172.1673	$172.17	$172.15	$172.20
7 purchase totals =	$723.96		$805.7540	$805.76	$805.75	$805.80