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	$227.38	13.667%	$258.456	$258.46	$258.45	$258.50
Purchase #2	$80.96	10.812%	$89.7134	$89.71	$89.70	$89.70
Purchase #3	$246.70	13.307%	$279.5284	$279.53	$279.55	$279.50
Purchase #4	$53.49	7.119%	$57.298	$57.30	$57.30	$57.30
Purchase #5	$55.92	7.555%	$60.1448	$60.14	$60.15	$60.10
Purchase #6	$135.95	11.182%	$151.1519	$151.15	$151.15	$151.20
Purchase #7	$9.69	3.847%	$10.0628	$10.06	$10.05	$10.10
7 purchase totals =	$810.09		$906.3553	$906.35	$906.35	$906.40