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	$113.64	8.814%	$123.6562	$123.66	$123.65	$123.70
Purchase #2	$37.57	10.614%	$41.5577	$41.56	$41.55	$41.60
Purchase #3	$155.40	6.338%	$165.2493	$165.25	$165.25	$165.20
Purchase #4	$82.85	8.349%	$89.7671	$89.77	$89.75	$89.80
Purchase #5	$120.48	8.228%	$130.3931	$130.39	$130.40	$130.40
Purchase #6	$33.42	8.230%	$36.1705	$36.17	$36.15	$36.20
Purchase #7	$9.73	12.116%	$10.9089	$10.91	$10.90	$10.90
7 purchase totals =	$553.09		$597.7028	$597.71	$597.65	$597.80