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	$56.74	12.576%	$63.8756	$63.88	$63.90	$63.90
Purchase #2	$74.43	10.603%	$82.3218	$82.32	$82.30	$82.30
Purchase #3	$126.92	13.461%	$144.0047	$144.00	$144.00	$144.00
Purchase #4	$36.79	9.220%	$40.182	$40.18	$40.20	$40.20
Purchase #5	$33.28	11.853%	$37.2247	$37.22	$37.20	$37.20
Purchase #6	$67.78	13.311%	$76.8022	$76.80	$76.80	$76.80
Purchase #7	$80.86	11.576%	$90.2204	$90.22	$90.20	$90.20
7 purchase totals =	$476.80		$534.6314	$534.62	$534.60	$534.60