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	$89.72	13.256%	$101.6133	$101.61	$101.60	$101.60
Purchase #2	$98.34	4.567%	$102.8312	$102.83	$102.85	$102.80
Purchase #3	$27.70	12.677%	$31.2115	$31.21	$31.20	$31.20
Purchase #4	$249.90	13.313%	$283.1692	$283.17	$283.15	$283.20
Purchase #5	$172.51	7.542%	$185.5207	$185.52	$185.50	$185.50
Purchase #6	$39.89	7.158%	$42.7453	$42.75	$42.75	$42.70
Purchase #7	$83.70	11.265%	$93.1288	$93.13	$93.15	$93.10
7 purchase totals =	$761.76		$840.2200	$840.22	$840.20	$840.10