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	$114.37	12.386%	$128.5359	$128.54	$128.55	$128.50
Purchase #2	$37.86	5.707%	$40.0207	$40.02	$40.00	$40.00
Purchase #3	$36.91	13.483%	$41.8866	$41.89	$41.90	$41.90
Purchase #4	$130.78	13.865%	$148.9126	$148.91	$148.90	$148.90
Purchase #5	$44.29	6.819%	$47.3101	$47.31	$47.30	$47.30
Purchase #6	$245.50	6.786%	$262.1596	$262.16	$262.15	$262.20
Purchase #7	$94.38	7.213%	$101.1876	$101.19	$101.20	$101.20
7 purchase totals =	$704.09		$770.0131	$770.02	$770.00	$770.00