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	$248.30	3.272%	$256.4244	$256.42	$256.40	$256.40
Purchase #2	$121.69	11.318%	$135.4629	$135.46	$135.45	$135.50
Purchase #3	$51.47	9.803%	$56.5156	$56.52	$56.50	$56.50
Purchase #4	$192.43	8.183%	$208.1765	$208.18	$208.20	$208.20
Purchase #5	$158.51	12.579%	$178.449	$178.45	$178.45	$178.40
Purchase #6	$84.53	7.520%	$90.8867	$90.89	$90.90	$90.90
Purchase #7	$73.62	11.443%	$82.0443	$82.04	$82.05	$82.00
7 purchase totals =	$930.55		$1,007.9594	$1,007.96	$1,007.95	$1,007.90