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	$107.25	12.260%	$120.3989	$120.40	$120.40	$120.40
Purchase #2	$109.35	12.139%	$122.624	$122.62	$122.60	$122.60
Purchase #3	$41.56	9.587%	$45.5444	$45.54	$45.55	$45.50
Purchase #4	$89.34	12.479%	$100.4887	$100.49	$100.50	$100.50
Purchase #5	$182.64	8.369%	$197.9251	$197.93	$197.95	$197.90
Purchase #6	$64.96	5.514%	$68.5419	$68.54	$68.55	$68.50
Purchase #7	$172.81	13.651%	$196.4003	$196.40	$196.40	$196.40
7 purchase totals =	$767.91		$851.9233	$851.92	$851.95	$851.80