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	$80.39	12.269%	$90.253	$90.25	$90.25	$90.30
Purchase #2	$48.59	5.430%	$51.2284	$51.23	$51.25	$51.20
Purchase #3	$88.29	6.718%	$94.2213	$94.22	$94.20	$94.20
Purchase #4	$221.83	11.451%	$247.2318	$247.23	$247.25	$247.20
Purchase #5	$240.86	8.382%	$261.0489	$261.05	$261.05	$261.00
Purchase #6	$9.31	10.693%	$10.3055	$10.31	$10.30	$10.30
Purchase #7	$95.29	4.753%	$99.8191	$99.82	$99.80	$99.80
7 purchase totals =	$784.56		$854.1080	$854.11	$854.10	$854.00