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	$50.43	13.155%	$57.0641	$57.06	$57.05	$57.10
Purchase #2	$49.38	12.382%	$55.4942	$55.49	$55.50	$55.50
Purchase #3	$18.25	10.430%	$20.1535	$20.15	$20.15	$20.20
Purchase #4	$141.29	4.412%	$147.5237	$147.52	$147.50	$147.50
Purchase #5	$168.34	6.703%	$179.6238	$179.62	$179.60	$179.60
Purchase #6	$26.42	9.103%	$28.825	$28.83	$28.85	$28.80
Purchase #7	$188.61	3.447%	$195.1114	$195.11	$195.10	$195.10
7 purchase totals =	$642.72		$683.7957	$683.78	$683.75	$683.80