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	$123.55	3.564%	$127.9533	$127.95	$127.95	$128.00
Purchase #2	$90.61	10.858%	$100.4484	$100.45	$100.45	$100.40
Purchase #3	$17.51	4.125%	$18.2323	$18.23	$18.25	$18.20
Purchase #4	$34.55	3.159%	$35.6414	$35.64	$35.65	$35.60
Purchase #5	$233.56	9.628%	$256.0472	$256.05	$256.05	$256.00
Purchase #6	$29.90	10.628%	$33.0778	$33.08	$33.10	$33.10
Purchase #7	$54.76	7.211%	$58.7087	$58.71	$58.70	$58.70
7 purchase totals =	$584.44		$630.1091	$630.11	$630.15	$630.00