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	$180.44	5.374%	$190.1368	$190.14	$190.15	$190.10
Purchase #2	$158.40	10.574%	$175.1492	$175.15	$175.15	$175.10
Purchase #3	$185.85	12.726%	$209.5013	$209.50	$209.50	$209.50
Purchase #4	$146.40	11.290%	$162.9286	$162.93	$162.95	$162.90
Purchase #5	$168.69	11.487%	$188.0674	$188.07	$188.05	$188.10
Purchase #6	$202.51	13.143%	$229.1259	$229.13	$229.15	$229.10
Purchase #7	$172.39	7.145%	$184.7073	$184.71	$184.70	$184.70
7 purchase totals =	$1,214.68		$1,339.6165	$1,339.63	$1,339.65	$1,339.50