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	$33.63	13.460%	$38.1566	$38.16	$38.15	$38.20
Purchase #2	$18.28	13.277%	$20.707	$20.71	$20.70	$20.70
Purchase #3	$137.93	11.222%	$153.4085	$153.41	$153.40	$153.40
Purchase #4	$52.56	12.780%	$59.2772	$59.28	$59.30	$59.30
Purchase #5	$200.72	12.474%	$225.7578	$225.76	$225.75	$225.80
Purchase #6	$38.57	4.228%	$40.2007	$40.20	$40.20	$40.20
Purchase #7	$187.92	6.626%	$200.3716	$200.37	$200.35	$200.40
7 purchase totals =	$669.61		$737.8794	$737.89	$737.85	$738.00