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	$10.64	13.241%	$12.0488	$12.05	$12.05	$12.00
Purchase #2	$6.50	9.222%	$7.0994	$7.10	$7.10	$7.10
Purchase #3	$77.53	12.263%	$87.0375	$87.04	$87.05	$87.00
Purchase #4	$98.32	6.621%	$104.8298	$104.83	$104.85	$104.80
Purchase #5	$121.59	8.799%	$132.2887	$132.29	$132.30	$132.30
Purchase #6	$143.63	5.316%	$151.2654	$151.27	$151.25	$151.30
Purchase #7	$155.45	12.263%	$174.5128	$174.51	$174.50	$174.50
7 purchase totals =	$613.66		$669.0824	$669.09	$669.10	$669.00