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	$62.70	13.340%	$71.0642	$71.06	$71.05	$71.10
Purchase #2	$155.35	11.584%	$173.3457	$173.35	$173.35	$173.30
Purchase #3	$118.90	3.850%	$123.4777	$123.48	$123.50	$123.50
Purchase #4	$7.37	6.756%	$7.8679	$7.87	$7.85	$7.90
Purchase #5	$186.25	7.281%	$199.8109	$199.81	$199.80	$199.80
Purchase #6	$151.47	3.136%	$156.2201	$156.22	$156.20	$156.20
Purchase #7	$113.51	10.557%	$125.4933	$125.49	$125.50	$125.50
7 purchase totals =	$795.55		$857.2798	$857.28	$857.25	$857.30