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	$14.67	5.653%	$15.4993	$15.50	$15.50	$15.50
Purchase #2	$42.71	6.838%	$45.6305	$45.63	$45.65	$45.60
Purchase #3	$177.54	7.523%	$190.8963	$190.90	$190.90	$190.90
Purchase #4	$147.85	11.499%	$164.8513	$164.85	$164.85	$164.90
Purchase #5	$62.87	11.672%	$70.2082	$70.21	$70.20	$70.20
Purchase #6	$133.54	8.843%	$145.3489	$145.35	$145.35	$145.30
Purchase #7	$149.73	10.781%	$165.8724	$165.87	$165.85	$165.90
7 purchase totals =	$728.91		$798.3069	$798.31	$798.30	$798.30