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	$65.90	7.193%	$70.6402	$70.64	$70.65	$70.60
Purchase #2	$200.82	11.300%	$223.5127	$223.51	$223.50	$223.50
Purchase #3	$238.75	10.718%	$264.3392	$264.34	$264.35	$264.30
Purchase #4	$55.36	5.325%	$58.3079	$58.31	$58.30	$58.30
Purchase #5	$153.48	11.616%	$171.3082	$171.31	$171.30	$171.30
Purchase #6	$216.97	9.468%	$237.5127	$237.51	$237.50	$237.50
Purchase #7	$71.54	3.514%	$74.0539	$74.05	$74.05	$74.10
7 purchase totals =	$1,002.82		$1,099.6748	$1,099.67	$1,099.65	$1,099.60