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	$238.47	7.707%	$256.8489	$256.85	$256.85	$256.80
Purchase #2	$159.32	8.799%	$173.3386	$173.34	$173.35	$173.30
Purchase #3	$83.71	7.809%	$90.2469	$90.25	$90.25	$90.20
Purchase #4	$102.75	7.473%	$110.4285	$110.43	$110.45	$110.40
Purchase #5	$200.46	3.674%	$207.8249	$207.82	$207.80	$207.80
Purchase #6	$165.51	8.189%	$179.0636	$179.06	$179.05	$179.10
Purchase #7	$237.43	8.678%	$258.0342	$258.03	$258.05	$258.00
7 purchase totals =	$1,187.65		$1,275.7856	$1,275.78	$1,275.80	$1,275.60