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	$36.31	11.113%	$40.3451	$40.35	$40.35	$40.30
Purchase #2	$80.36	3.217%	$82.9452	$82.95	$82.95	$82.90
Purchase #3	$222.86	12.830%	$251.4529	$251.45	$251.45	$251.50
Purchase #4	$160.50	8.452%	$174.0655	$174.07	$174.05	$174.10
Purchase #5	$140.40	13.184%	$158.9103	$158.91	$158.90	$158.90
Purchase #6	$216.66	10.445%	$239.2901	$239.29	$239.30	$239.30
Purchase #7	$214.76	8.656%	$233.3496	$233.35	$233.35	$233.30
7 purchase totals =	$1,071.85		$1,180.3587	$1,180.37	$1,180.35	$1,180.30