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	$15.40	9.635%	$16.8838	$16.88	$16.90	$16.90
Purchase #2	$66.33	7.653%	$71.4062	$71.41	$71.40	$71.40
Purchase #3	$195.58	4.540%	$204.4593	$204.46	$204.45	$204.50
Purchase #4	$145.45	3.748%	$150.9015	$150.90	$150.90	$150.90
Purchase #5	$98.85	12.574%	$111.2794	$111.28	$111.30	$111.30
Purchase #6	$67.92	10.103%	$74.782	$74.78	$74.80	$74.80
Purchase #7	$199.34	11.380%	$222.0249	$222.02	$222.00	$222.00
7 purchase totals =	$788.87		$851.7371	$851.73	$851.75	$851.80