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	$11.71	6.171%	$12.4326	$12.43	$12.45	$12.40
Purchase #2	$102.78	10.508%	$113.5801	$113.58	$113.60	$113.60
Purchase #3	$100.48	9.235%	$109.7593	$109.76	$109.75	$109.80
Purchase #4	$182.44	10.829%	$202.1964	$202.20	$202.20	$202.20
Purchase #5	$36.41	3.238%	$37.589	$37.59	$37.60	$37.60
Purchase #6	$204.29	9.179%	$223.0418	$223.04	$223.05	$223.00
Purchase #7	$222.45	9.665%	$243.9498	$243.95	$243.95	$243.90
7 purchase totals =	$860.56		$942.5490	$942.55	$942.60	$942.50