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	$138.25	6.283%	$146.9362	$146.94	$146.95	$146.90
Purchase #2	$25.62	12.475%	$28.8161	$28.82	$28.80	$28.80
Purchase #3	$33.34	12.302%	$37.4415	$37.44	$37.45	$37.40
Purchase #4	$134.34	6.577%	$143.1755	$143.18	$143.20	$143.20
Purchase #5	$59.33	12.770%	$66.9064	$66.91	$66.90	$66.90
Purchase #6	$39.91	11.613%	$44.5447	$44.54	$44.55	$44.50
Purchase #7	$50.54	5.366%	$53.252	$53.25	$53.25	$53.30
7 purchase totals =	$481.33		$521.0724	$521.08	$521.10	$521.00