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	$39.85	13.820%	$45.3573	$45.36	$45.35	$45.40
Purchase #2	$52.88	13.313%	$59.9199	$59.92	$59.90	$59.90
Purchase #3	$86.77	12.348%	$97.4844	$97.48	$97.50	$97.50
Purchase #4	$147.44	5.156%	$155.042	$155.04	$155.05	$155.00
Purchase #5	$243.80	10.724%	$269.9451	$269.95	$269.95	$269.90
Purchase #6	$69.61	6.461%	$74.1075	$74.11	$74.10	$74.10
Purchase #7	$190.95	4.763%	$200.0449	$200.04	$200.05	$200.00
7 purchase totals =	$831.30		$901.9011	$901.90	$901.90	$901.80