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	$83.81	5.827%	$88.6936	$88.69	$88.70	$88.70
Purchase #2	$82.90	6.598%	$88.3697	$88.37	$88.35	$88.40
Purchase #3	$97.40	12.837%	$109.9032	$109.90	$109.90	$109.90
Purchase #4	$77.94	11.556%	$86.9467	$86.95	$86.95	$86.90
Purchase #5	$74.74	9.405%	$81.7693	$81.77	$81.75	$81.80
Purchase #6	$58.45	5.275%	$61.5332	$61.53	$61.55	$61.50
Purchase #7	$33.94	4.230%	$35.3757	$35.38	$35.40	$35.40
7 purchase totals =	$509.18		$552.5914	$552.59	$552.60	$552.60