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	$198.42	13.407%	$225.0222	$225.02	$225.00	$225.00
Purchase #2	$80.80	5.303%	$85.0848	$85.08	$85.10	$85.10
Purchase #3	$139.80	6.188%	$148.4508	$148.45	$148.45	$148.50
Purchase #4	$192.95	10.302%	$212.8277	$212.83	$212.85	$212.80
Purchase #5	$49.33	12.202%	$55.3492	$55.35	$55.35	$55.30
Purchase #6	$53.34	10.870%	$59.1381	$59.14	$59.15	$59.10
Purchase #7	$180.33	13.196%	$204.1263	$204.13	$204.15	$204.10
7 purchase totals =	$894.97		$989.9991	$990.00	$990.05	$989.90