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	$88.59	6.387%	$94.2482	$94.25	$94.25	$94.20
Purchase #2	$187.59	12.105%	$210.2978	$210.30	$210.30	$210.30
Purchase #3	$54.73	10.689%	$60.5801	$60.58	$60.60	$60.60
Purchase #4	$64.43	4.492%	$67.3242	$67.32	$67.30	$67.30
Purchase #5	$172.65	9.417%	$188.9085	$188.91	$188.90	$188.90
Purchase #6	$131.77	13.866%	$150.0412	$150.04	$150.05	$150.00
Purchase #7	$34.47	6.710%	$36.7829	$36.78	$36.80	$36.80
7 purchase totals =	$734.23		$808.1829	$808.18	$808.20	$808.10