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	$152.90	11.340%	$170.2389	$170.24	$170.25	$170.20
Purchase #2	$145.32	3.256%	$150.0516	$150.05	$150.05	$150.10
Purchase #3	$67.94	4.686%	$71.1237	$71.12	$71.10	$71.10
Purchase #4	$152.46	12.205%	$171.0677	$171.07	$171.05	$171.10
Purchase #5	$11.47	11.730%	$12.8154	$12.82	$12.80	$12.80
Purchase #6	$102.95	3.377%	$106.4266	$106.43	$106.45	$106.40
Purchase #7	$101.79	7.190%	$109.1087	$109.11	$109.10	$109.10
7 purchase totals =	$734.83		$790.8326	$790.84	$790.80	$790.80