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	$80.43	10.819%	$89.1317	$89.13	$89.15	$89.10
Purchase #2	$236.89	7.181%	$253.9011	$253.90	$253.90	$253.90
Purchase #3	$227.38	5.855%	$240.6931	$240.69	$240.70	$240.70
Purchase #4	$202.53	9.261%	$221.2863	$221.29	$221.30	$221.30
Purchase #5	$55.29	6.843%	$59.0735	$59.07	$59.05	$59.10
Purchase #6	$228.58	13.859%	$260.2589	$260.26	$260.25	$260.30
Purchase #7	$111.26	11.184%	$123.7033	$123.70	$123.70	$123.70
7 purchase totals =	$1,142.36		$1,248.0479	$1,248.04	$1,248.05	$1,248.10