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	$123.36	4.554%	$128.9778	$128.98	$129.00	$129.00
Purchase #2	$40.84	5.562%	$43.1115	$43.11	$43.10	$43.10
Purchase #3	$175.89	8.841%	$191.4404	$191.44	$191.45	$191.40
Purchase #4	$230.43	6.110%	$244.5093	$244.51	$244.50	$244.50
Purchase #5	$217.64	7.429%	$233.8085	$233.81	$233.80	$233.80
Purchase #6	$78.86	13.295%	$89.3444	$89.34	$89.35	$89.30
Purchase #7	$106.77	11.223%	$118.7528	$118.75	$118.75	$118.80
7 purchase totals =	$973.79		$1,049.9447	$1,049.94	$1,049.95	$1,049.90