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	$83.61	9.134%	$91.2469	$91.25	$91.25	$91.20
Purchase #2	$156.54	5.736%	$165.5191	$165.52	$165.50	$165.50
Purchase #3	$13.64	5.675%	$14.4141	$14.41	$14.40	$14.40
Purchase #4	$42.98	11.823%	$48.0615	$48.06	$48.05	$48.10
Purchase #5	$113.29	7.490%	$121.7754	$121.78	$121.80	$121.80
Purchase #6	$116.99	12.721%	$131.8723	$131.87	$131.85	$131.90
Purchase #7	$55.53	3.425%	$57.4319	$57.43	$57.45	$57.40
7 purchase totals =	$582.58		$630.3212	$630.32	$630.30	$630.30