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	$120.30	3.500%	$124.5105	$124.51	$124.50	$124.50
Purchase #2	$122.94	3.645%	$127.4212	$127.42	$127.40	$127.40
Purchase #3	$156.50	10.166%	$172.4098	$172.41	$172.40	$172.40
Purchase #4	$149.90	6.151%	$159.1203	$159.12	$159.10	$159.10
Purchase #5	$244.68	12.748%	$275.8718	$275.87	$275.85	$275.90
Purchase #6	$6.76	4.428%	$7.0593	$7.06	$7.05	$7.10
Purchase #7	$182.67	4.209%	$190.3586	$190.36	$190.35	$190.40
7 purchase totals =	$983.75		$1,056.7515	$1,056.75	$1,056.65	$1,056.80