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	$167.38	3.561%	$173.3404	$173.34	$173.35	$173.30
Purchase #2	$37.82	9.582%	$41.4439	$41.44	$41.45	$41.40
Purchase #3	$247.48	9.281%	$270.4486	$270.45	$270.45	$270.40
Purchase #4	$204.42	13.680%	$232.3847	$232.38	$232.40	$232.40
Purchase #5	$244.30	10.180%	$269.1697	$269.17	$269.15	$269.20
Purchase #6	$10.38	6.474%	$11.052	$11.05	$11.05	$11.10
Purchase #7	$14.56	6.427%	$15.4958	$15.50	$15.50	$15.50
7 purchase totals =	$926.34		$1,013.3351	$1,013.33	$1,013.35	$1,013.30