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	$116.90	6.558%	$124.5663	$124.57	$124.55	$124.60
Purchase #2	$50.40	6.845%	$53.8499	$53.85	$53.85	$53.80
Purchase #3	$243.79	8.530%	$264.5853	$264.59	$264.60	$264.60
Purchase #4	$111.95	6.253%	$118.9502	$118.95	$118.95	$119.00
Purchase #5	$13.29	11.529%	$14.8222	$14.82	$14.80	$14.80
Purchase #6	$33.48	11.806%	$37.4326	$37.43	$37.45	$37.40
Purchase #7	$150.74	9.857%	$165.5984	$165.60	$165.60	$165.60
7 purchase totals =	$720.55		$779.8049	$779.81	$779.80	$779.80