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	$153.86	8.113%	$166.3427	$166.34	$166.35	$166.30
Purchase #2	$30.36	9.371%	$33.205	$33.21	$33.20	$33.20
Purchase #3	$50.57	13.484%	$57.3889	$57.39	$57.40	$57.40
Purchase #4	$53.70	11.395%	$59.8191	$59.82	$59.80	$59.80
Purchase #5	$75.40	4.862%	$79.0659	$79.07	$79.05	$79.10
Purchase #6	$80.44	11.282%	$89.5152	$89.52	$89.50	$89.50
Purchase #7	$173.81	8.599%	$188.7559	$188.76	$188.75	$188.80
7 purchase totals =	$618.14		$674.0927	$674.11	$674.05	$674.10