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	$211.52	6.321%	$224.8902	$224.89	$224.90	$224.90
Purchase #2	$242.99	5.619%	$256.6436	$256.64	$256.65	$256.60
Purchase #3	$155.57	11.576%	$173.5788	$173.58	$173.60	$173.60
Purchase #4	$58.73	5.612%	$62.0259	$62.03	$62.05	$62.00
Purchase #5	$91.63	11.556%	$102.2188	$102.22	$102.20	$102.20
Purchase #6	$42.47	7.369%	$45.5996	$45.60	$45.60	$45.60
Purchase #7	$121.83	13.701%	$138.5219	$138.52	$138.50	$138.50
7 purchase totals =	$924.74		$1,003.4788	$1,003.48	$1,003.50	$1,003.40