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	$37.76	11.371%	$42.0537	$42.05	$42.05	$42.10
Purchase #2	$78.29	11.653%	$87.4131	$87.41	$87.40	$87.40
Purchase #3	$77.85	9.399%	$85.1671	$85.17	$85.15	$85.20
Purchase #4	$218.74	11.158%	$243.147	$243.15	$243.15	$243.10
Purchase #5	$174.81	9.221%	$190.9292	$190.93	$190.95	$190.90
Purchase #6	$121.84	10.403%	$134.515	$134.52	$134.50	$134.50
Purchase #7	$11.57	10.530%	$12.7883	$12.79	$12.80	$12.80
7 purchase totals =	$720.86		$796.0134	$796.02	$796.00	$796.00