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	$157.85	8.380%	$171.0778	$171.08	$171.10	$171.10
Purchase #2	$30.28	7.844%	$32.6552	$32.66	$32.65	$32.70
Purchase #3	$54.40	11.497%	$60.6544	$60.65	$60.65	$60.70
Purchase #4	$140.73	7.709%	$151.5789	$151.58	$151.60	$151.60
Purchase #5	$99.80	11.658%	$111.4347	$111.43	$111.45	$111.40
Purchase #6	$78.48	11.767%	$87.7147	$87.71	$87.70	$87.70
Purchase #7	$57.84	11.450%	$64.4627	$64.46	$64.45	$64.50
7 purchase totals =	$619.38		$679.5784	$679.57	$679.60	$679.70