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	$113.49	6.370%	$120.7193	$120.72	$120.70	$120.70
Purchase #2	$175.61	11.557%	$195.9052	$195.91	$195.90	$195.90
Purchase #3	$70.60	11.184%	$78.4959	$78.50	$78.50	$78.50
Purchase #4	$184.95	3.294%	$191.0423	$191.04	$191.05	$191.00
Purchase #5	$94.67	11.826%	$105.8657	$105.87	$105.85	$105.90
Purchase #6	$165.48	13.619%	$188.0167	$188.02	$188.00	$188.00
Purchase #7	$234.56	11.779%	$262.1888	$262.19	$262.20	$262.20
7 purchase totals =	$1,039.36		$1,142.2339	$1,142.25	$1,142.20	$1,142.20