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	$53.49	7.166%	$57.3231	$57.32	$57.30	$57.30
Purchase #2	$48.54	7.742%	$52.298	$52.30	$52.30	$52.30
Purchase #3	$16.56	11.316%	$18.4339	$18.43	$18.45	$18.40
Purchase #4	$46.35	10.143%	$51.0513	$51.05	$51.05	$51.10
Purchase #5	$113.80	5.413%	$119.96	$119.96	$119.95	$120.00
Purchase #6	$144.68	9.467%	$158.3769	$158.38	$158.40	$158.40
Purchase #7	$76.54	8.561%	$83.0926	$83.09	$83.10	$83.10
7 purchase totals =	$499.96		$540.5358	$540.53	$540.55	$540.60