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	$11.27	10.306%	$12.4315	$12.43	$12.45	$12.40
Purchase #2	$245.81	4.226%	$256.1979	$256.20	$256.20	$256.20
Purchase #3	$150.57	3.121%	$155.2693	$155.27	$155.25	$155.30
Purchase #4	$53.25	11.183%	$59.2049	$59.20	$59.20	$59.20
Purchase #5	$122.53	7.158%	$131.3007	$131.30	$131.30	$131.30
Purchase #6	$9.84	8.423%	$10.6688	$10.67	$10.65	$10.70
Purchase #7	$159.97	4.111%	$166.5464	$166.55	$166.55	$166.50
7 purchase totals =	$753.24		$791.6195	$791.62	$791.60	$791.60