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	$85.82	5.593%	$90.6199	$90.62	$90.60	$90.60
Purchase #2	$236.94	10.306%	$261.359	$261.36	$261.35	$261.40
Purchase #3	$221.44	5.775%	$234.2282	$234.23	$234.25	$234.20
Purchase #4	$78.30	5.859%	$82.8876	$82.89	$82.90	$82.90
Purchase #5	$19.59	5.276%	$20.6236	$20.62	$20.60	$20.60
Purchase #6	$242.43	6.607%	$258.4474	$258.45	$258.45	$258.40
Purchase #7	$75.42	10.859%	$83.6099	$83.61	$83.60	$83.60
7 purchase totals =	$959.94		$1,031.7756	$1,031.78	$1,031.75	$1,031.70