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	$65.79	12.743%	$74.1736	$74.17	$74.15	$74.20
Purchase #2	$47.54	5.294%	$50.0568	$50.06	$50.05	$50.10
Purchase #3	$72.54	7.113%	$77.6998	$77.70	$77.70	$77.70
Purchase #4	$92.36	9.628%	$101.2524	$101.25	$101.25	$101.30
Purchase #5	$40.29	6.236%	$42.8025	$42.80	$42.80	$42.80
Purchase #6	$131.92	13.648%	$149.9244	$149.92	$149.90	$149.90
Purchase #7	$54.72	8.664%	$59.4609	$59.46	$59.45	$59.50
7 purchase totals =	$505.16		$555.3704	$555.36	$555.30	$555.50