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	$205.34	4.130%	$213.8205	$213.82	$213.80	$213.80
Purchase #2	$111.98	7.551%	$120.4356	$120.44	$120.45	$120.40
Purchase #3	$156.28	12.260%	$175.4399	$175.44	$175.45	$175.40
Purchase #4	$79.67	9.463%	$87.2092	$87.21	$87.20	$87.20
Purchase #5	$93.46	13.303%	$105.893	$105.89	$105.90	$105.90
Purchase #6	$128.73	11.298%	$143.2739	$143.27	$143.25	$143.30
Purchase #7	$138.86	4.372%	$144.931	$144.93	$144.95	$144.90
7 purchase totals =	$914.32		$991.0031	$991.00	$991.00	$990.90