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	$200.41	8.800%	$218.0461	$218.05	$218.05	$218.00
Purchase #2	$125.83	10.182%	$138.642	$138.64	$138.65	$138.60
Purchase #3	$6.48	11.322%	$7.2137	$7.21	$7.20	$7.20
Purchase #4	$99.62	11.216%	$110.7934	$110.79	$110.80	$110.80
Purchase #5	$102.46	9.149%	$111.8341	$111.83	$111.85	$111.80
Purchase #6	$89.89	13.320%	$101.8633	$101.86	$101.85	$101.90
Purchase #7	$155.77	6.381%	$165.7097	$165.71	$165.70	$165.70
7 purchase totals =	$780.46		$854.1023	$854.09	$854.10	$854.00