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	$22.89	7.150%	$24.5266	$24.53	$24.55	$24.50
Purchase #2	$23.51	5.325%	$24.7619	$24.76	$24.75	$24.80
Purchase #3	$172.49	7.183%	$184.88	$184.88	$184.90	$184.90
Purchase #4	$40.81	10.257%	$44.9959	$45.00	$45.00	$45.00
Purchase #5	$10.98	13.318%	$12.4423	$12.44	$12.45	$12.40
Purchase #6	$89.83	10.584%	$99.3376	$99.34	$99.35	$99.30
Purchase #7	$249.52	12.795%	$281.4461	$281.45	$281.45	$281.40
7 purchase totals =	$610.03		$672.3904	$672.40	$672.45	$672.30