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	$124.40	8.168%	$134.561	$134.56	$134.55	$134.60
Purchase #2	$107.67	4.515%	$112.5313	$112.53	$112.55	$112.50
Purchase #3	$225.62	13.103%	$255.183	$255.18	$255.20	$255.20
Purchase #4	$59.46	9.614%	$65.1765	$65.18	$65.20	$65.20
Purchase #5	$139.25	13.594%	$158.1796	$158.18	$158.20	$158.20
Purchase #6	$178.62	11.302%	$198.8076	$198.81	$198.80	$198.80
Purchase #7	$32.76	13.863%	$37.3015	$37.30	$37.30	$37.30
7 purchase totals =	$867.78		$961.7405	$961.74	$961.80	$961.80