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	$100.86	10.316%	$111.2647	$111.26	$111.25	$111.30
Purchase #2	$196.95	13.412%	$223.3649	$223.36	$223.35	$223.40
Purchase #3	$111.30	9.222%	$121.5641	$121.56	$121.55	$121.60
Purchase #4	$149.81	7.402%	$160.8989	$160.90	$160.90	$160.90
Purchase #5	$45.28	11.723%	$50.5882	$50.59	$50.60	$50.60
Purchase #6	$91.28	3.308%	$94.2995	$94.30	$94.30	$94.30
Purchase #7	$37.43	12.442%	$42.087	$42.09	$42.10	$42.10
7 purchase totals =	$732.91		$804.0673	$804.06	$804.05	$804.20