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	$188.25	12.504%	$211.7888	$211.79	$211.80	$211.80
Purchase #2	$32.77	9.533%	$35.894	$35.89	$35.90	$35.90
Purchase #3	$59.74	3.263%	$61.6893	$61.69	$61.70	$61.70
Purchase #4	$122.76	11.163%	$136.4637	$136.46	$136.45	$136.50
Purchase #5	$205.66	5.861%	$217.7137	$217.71	$217.70	$217.70
Purchase #6	$223.92	11.655%	$250.0179	$250.02	$250.00	$250.00
Purchase #7	$81.42	13.740%	$92.6071	$92.61	$92.60	$92.60
7 purchase totals =	$914.52		$1,006.1745	$1,006.17	$1,006.15	$1,006.20