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	$90.38	11.498%	$100.7719	$100.77	$100.75	$100.80
Purchase #2	$73.71	12.513%	$82.9333	$82.93	$82.95	$82.90
Purchase #3	$172.82	3.175%	$178.307	$178.31	$178.30	$178.30
Purchase #4	$223.42	12.265%	$250.8225	$250.82	$250.80	$250.80
Purchase #5	$42.54	13.225%	$48.1659	$48.17	$48.15	$48.20
Purchase #6	$114.99	6.420%	$122.3724	$122.37	$122.35	$122.40
Purchase #7	$203.50	5.324%	$214.3343	$214.33	$214.35	$214.30
7 purchase totals =	$921.36		$997.7073	$997.70	$997.65	$997.70