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	$142.79	6.258%	$151.7258	$151.73	$151.75	$151.70
Purchase #2	$75.39	11.314%	$83.9196	$83.92	$83.90	$83.90
Purchase #3	$201.33	10.277%	$222.0207	$222.02	$222.00	$222.00
Purchase #4	$154.94	13.613%	$176.032	$176.03	$176.05	$176.00
Purchase #5	$71.59	10.228%	$78.9122	$78.91	$78.90	$78.90
Purchase #6	$27.78	6.530%	$29.594	$29.59	$29.60	$29.60
Purchase #7	$229.60	8.670%	$249.5063	$249.51	$249.50	$249.50
7 purchase totals =	$903.42		$991.7106	$991.71	$991.70	$991.60