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	$92.58	7.126%	$99.1773	$99.18	$99.20	$99.20
Purchase #2	$177.57	6.645%	$189.3695	$189.37	$189.35	$189.40
Purchase #3	$94.88	9.223%	$103.6308	$103.63	$103.65	$103.60
Purchase #4	$29.86	9.128%	$32.5856	$32.59	$32.60	$32.60
Purchase #5	$82.28	8.613%	$89.3668	$89.37	$89.35	$89.40
Purchase #6	$131.39	12.804%	$148.2132	$148.21	$148.20	$148.20
Purchase #7	$9.80	4.325%	$10.2239	$10.22	$10.20	$10.20
7 purchase totals =	$618.36		$672.5671	$672.57	$672.55	$672.60