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	$50.78	13.113%	$57.4388	$57.44	$57.45	$57.40
Purchase #2	$31.34	6.723%	$33.447	$33.45	$33.45	$33.40
Purchase #3	$131.41	11.306%	$146.2672	$146.27	$146.25	$146.30
Purchase #4	$219.44	12.592%	$247.0719	$247.07	$247.05	$247.10
Purchase #5	$89.33	10.867%	$99.0375	$99.04	$99.05	$99.00
Purchase #6	$151.31	9.676%	$165.9508	$165.95	$165.95	$166.00
Purchase #7	$63.82	8.351%	$69.1496	$69.15	$69.15	$69.10
7 purchase totals =	$737.43		$818.3628	$818.37	$818.35	$818.30