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	$150.38	3.313%	$155.3621	$155.36	$155.35	$155.40
Purchase #2	$231.52	10.298%	$255.3619	$255.36	$255.35	$255.40
Purchase #3	$88.92	13.669%	$101.0745	$101.07	$101.05	$101.10
Purchase #4	$78.25	5.331%	$82.4215	$82.42	$82.40	$82.40
Purchase #5	$50.56	9.725%	$55.477	$55.48	$55.50	$55.50
Purchase #6	$32.93	13.221%	$37.2837	$37.28	$37.30	$37.30
Purchase #7	$64.63	10.143%	$71.1854	$71.19	$71.20	$71.20
7 purchase totals =	$697.19		$758.1661	$758.16	$758.15	$758.30