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	$139.91	7.219%	$150.0101	$150.01	$150.00	$150.00
Purchase #2	$202.31	9.640%	$221.8127	$221.81	$221.80	$221.80
Purchase #3	$9.79	10.549%	$10.8227	$10.82	$10.80	$10.80
Purchase #4	$115.42	13.589%	$131.1044	$131.10	$131.10	$131.10
Purchase #5	$48.53	11.439%	$54.0813	$54.08	$54.10	$54.10
Purchase #6	$42.92	7.572%	$46.1699	$46.17	$46.15	$46.20
Purchase #7	$83.69	9.287%	$91.4623	$91.46	$91.45	$91.50
7 purchase totals =	$642.57		$705.4634	$705.45	$705.40	$705.50