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	$123.45	11.131%	$137.1912	$137.19	$137.20	$137.20
Purchase #2	$40.95	6.241%	$43.5057	$43.51	$43.50	$43.50
Purchase #3	$50.29	6.405%	$53.5111	$53.51	$53.50	$53.50
Purchase #4	$79.80	3.589%	$82.664	$82.66	$82.65	$82.70
Purchase #5	$131.81	13.405%	$149.4791	$149.48	$149.50	$149.50
Purchase #6	$170.79	11.149%	$189.8314	$189.83	$189.85	$189.80
Purchase #7	$178.95	11.767%	$200.007	$200.01	$200.00	$200.00
7 purchase totals =	$776.04		$856.1895	$856.19	$856.20	$856.20