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	$66.45	5.592%	$70.1659	$70.17	$70.15	$70.20
Purchase #2	$87.41	5.648%	$92.3469	$92.35	$92.35	$92.30
Purchase #3	$196.33	6.232%	$208.5653	$208.57	$208.55	$208.60
Purchase #4	$225.47	13.365%	$255.6041	$255.60	$255.60	$255.60
Purchase #5	$68.71	3.367%	$71.0235	$71.02	$71.00	$71.00
Purchase #6	$94.53	5.546%	$99.7726	$99.77	$99.75	$99.80
Purchase #7	$129.26	10.735%	$143.1361	$143.14	$143.15	$143.10
7 purchase totals =	$868.16		$940.6144	$940.62	$940.55	$940.60