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	$242.73	4.279%	$253.1164	$253.12	$253.10	$253.10
Purchase #2	$99.72	11.641%	$111.3284	$111.33	$111.35	$111.30
Purchase #3	$54.67	12.674%	$61.5989	$61.60	$61.60	$61.60
Purchase #4	$139.26	6.341%	$148.0905	$148.09	$148.10	$148.10
Purchase #5	$36.54	10.380%	$40.3329	$40.33	$40.35	$40.30
Purchase #6	$204.42	13.645%	$232.3131	$232.31	$232.30	$232.30
Purchase #7	$116.78	10.842%	$129.4413	$129.44	$129.45	$129.40
7 purchase totals =	$894.12		$976.2215	$976.22	$976.25	$976.10