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	$100.55	5.251%	$105.8299	$105.83	$105.85	$105.80
Purchase #2	$223.65	13.531%	$253.9121	$253.91	$253.90	$253.90
Purchase #3	$131.42	8.359%	$142.4054	$142.41	$142.40	$142.40
Purchase #4	$31.39	8.225%	$33.9718	$33.97	$33.95	$34.00
Purchase #5	$166.74	7.795%	$179.7374	$179.74	$179.75	$179.70
Purchase #6	$36.45	10.169%	$40.1566	$40.16	$40.15	$40.20
Purchase #7	$109.47	12.512%	$123.1669	$123.17	$123.15	$123.20
7 purchase totals =	$799.67		$879.1801	$879.19	$879.15	$879.20