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	$74.82	8.754%	$81.3697	$81.37	$81.35	$81.40
Purchase #2	$127.91	9.332%	$139.8466	$139.85	$139.85	$139.80
Purchase #3	$132.94	13.474%	$150.8523	$150.85	$150.85	$150.90
Purchase #4	$31.43	9.459%	$34.403	$34.40	$34.40	$34.40
Purchase #5	$205.57	8.568%	$223.1832	$223.18	$223.20	$223.20
Purchase #6	$232.89	10.232%	$256.7193	$256.72	$256.70	$256.70
Purchase #7	$170.32	5.567%	$179.8017	$179.80	$179.80	$179.80
7 purchase totals =	$975.88		$1,066.1758	$1,066.17	$1,066.15	$1,066.20