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	$112.70	7.504%	$121.157	$121.16	$121.15	$121.20
Purchase #2	$155.54	8.151%	$168.2181	$168.22	$168.20	$168.20
Purchase #3	$128.85	11.261%	$143.3598	$143.36	$143.35	$143.40
Purchase #4	$162.36	6.471%	$172.8663	$172.87	$172.85	$172.90
Purchase #5	$250.36	7.829%	$269.9607	$269.96	$269.95	$270.00
Purchase #6	$169.33	11.868%	$189.4261	$189.43	$189.45	$189.40
Purchase #7	$69.68	9.823%	$76.5247	$76.52	$76.50	$76.50
7 purchase totals =	$1,048.82		$1,141.5127	$1,141.52	$1,141.45	$1,141.60