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	$37.89	8.611%	$41.1527	$41.15	$41.15	$41.20
Purchase #2	$62.83	11.444%	$70.0203	$70.02	$70.00	$70.00
Purchase #3	$117.50	5.589%	$124.0671	$124.07	$124.05	$124.10
Purchase #4	$186.46	11.639%	$208.1621	$208.16	$208.15	$208.20
Purchase #5	$52.89	9.511%	$57.9204	$57.92	$57.90	$57.90
Purchase #6	$7.32	5.425%	$7.7171	$7.72	$7.70	$7.70
Purchase #7	$143.31	10.688%	$158.627	$158.63	$158.65	$158.60
7 purchase totals =	$608.20		$667.6667	$667.67	$667.60	$667.70