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	$45.46	7.203%	$48.7345	$48.73	$48.75	$48.70
Purchase #2	$202.96	10.125%	$223.5097	$223.51	$223.50	$223.50
Purchase #3	$249.90	13.581%	$283.8389	$283.84	$283.85	$283.80
Purchase #4	$90.67	11.244%	$100.8649	$100.86	$100.85	$100.90
Purchase #5	$71.94	5.702%	$76.042	$76.04	$76.05	$76.00
Purchase #6	$55.96	12.184%	$62.7782	$62.78	$62.80	$62.80
Purchase #7	$101.78	13.529%	$115.5498	$115.55	$115.55	$115.50
7 purchase totals =	$818.67		$911.3180	$911.31	$911.35	$911.20