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	$38.47	10.664%	$42.5724	$42.57	$42.55	$42.60
Purchase #2	$64.78	10.697%	$71.7095	$71.71	$71.70	$71.70
Purchase #3	$146.25	4.761%	$153.213	$153.21	$153.20	$153.20
Purchase #4	$30.50	7.807%	$32.8811	$32.88	$32.90	$32.90
Purchase #5	$115.58	8.214%	$125.0737	$125.07	$125.05	$125.10
Purchase #6	$206.59	7.745%	$222.5904	$222.59	$222.60	$222.60
Purchase #7	$220.46	4.858%	$231.1699	$231.17	$231.15	$231.20
7 purchase totals =	$822.63		$879.2100	$879.20	$879.15	$879.30