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	$37.58	8.709%	$40.8528	$40.85	$40.85	$40.90
Purchase #2	$6.67	12.172%	$7.4819	$7.48	$7.50	$7.50
Purchase #3	$171.50	10.344%	$189.24	$189.24	$189.25	$189.20
Purchase #4	$110.79	10.192%	$122.0817	$122.08	$122.10	$122.10
Purchase #5	$178.60	4.385%	$186.4316	$186.43	$186.45	$186.40
Purchase #6	$189.78	9.659%	$208.1109	$208.11	$208.10	$208.10
Purchase #7	$207.31	7.154%	$222.141	$222.14	$222.15	$222.10
7 purchase totals =	$902.23		$976.3399	$976.33	$976.40	$976.30