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	$48.51	12.487%	$54.5674	$54.57	$54.55	$54.60
Purchase #2	$245.57	12.667%	$276.6764	$276.68	$276.70	$276.70
Purchase #3	$123.68	3.693%	$128.2475	$128.25	$128.25	$128.20
Purchase #4	$81.95	9.402%	$89.6549	$89.65	$89.65	$89.70
Purchase #5	$100.50	5.757%	$106.2858	$106.29	$106.30	$106.30
Purchase #6	$230.62	7.245%	$247.3284	$247.33	$247.35	$247.30
Purchase #7	$123.42	3.275%	$127.462	$127.46	$127.45	$127.50
7 purchase totals =	$954.25		$1,030.2224	$1,030.23	$1,030.25	$1,030.30