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	$215.48	8.223%	$233.1989	$233.20	$233.20	$233.20
Purchase #2	$85.36	4.595%	$89.2823	$89.28	$89.30	$89.30
Purchase #3	$238.25	11.601%	$265.8894	$265.89	$265.90	$265.90
Purchase #4	$33.90	4.785%	$35.5221	$35.52	$35.50	$35.50
Purchase #5	$201.50	12.576%	$226.8406	$226.84	$226.85	$226.80
Purchase #6	$35.28	10.730%	$39.0655	$39.07	$39.05	$39.10
Purchase #7	$232.45	12.255%	$260.9367	$260.94	$260.95	$260.90
7 purchase totals =	$1,042.22		$1,150.7355	$1,150.74	$1,150.75	$1,150.70