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	$42.31	9.488%	$46.3244	$46.32	$46.30	$46.30
Purchase #2	$146.37	4.165%	$152.4663	$152.47	$152.45	$152.50
Purchase #3	$147.29	9.350%	$161.0616	$161.06	$161.05	$161.10
Purchase #4	$192.35	6.754%	$205.3413	$205.34	$205.35	$205.30
Purchase #5	$30.85	11.220%	$34.3114	$34.31	$34.30	$34.30
Purchase #6	$56.71	5.220%	$59.6703	$59.67	$59.65	$59.70
Purchase #7	$231.57	4.424%	$241.8147	$241.81	$241.80	$241.80
7 purchase totals =	$847.45		$900.9900	$900.98	$900.90	$901.00