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	$68.86	13.780%	$78.3489	$78.35	$78.35	$78.30
Purchase #2	$142.77	5.609%	$150.778	$150.78	$150.80	$150.80
Purchase #3	$76.38	11.338%	$85.04	$85.04	$85.05	$85.00
Purchase #4	$19.57	13.514%	$22.2147	$22.21	$22.20	$22.20
Purchase #5	$163.44	3.340%	$168.8989	$168.90	$168.90	$168.90
Purchase #6	$164.57	4.693%	$172.2933	$172.29	$172.30	$172.30
Purchase #7	$115.32	9.738%	$126.5499	$126.55	$126.55	$126.50
7 purchase totals =	$750.91		$804.1237	$804.12	$804.15	$804.00