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	$78.86	6.392%	$83.9007	$83.90	$83.90	$83.90
Purchase #2	$44.81	4.188%	$46.6866	$46.69	$46.70	$46.70
Purchase #3	$240.77	10.276%	$265.5115	$265.51	$265.50	$265.50
Purchase #4	$89.50	9.118%	$97.6606	$97.66	$97.65	$97.70
Purchase #5	$245.86	7.741%	$264.892	$264.89	$264.90	$264.90
Purchase #6	$172.83	10.308%	$190.6453	$190.65	$190.65	$190.60
Purchase #7	$44.95	12.707%	$50.6618	$50.66	$50.65	$50.70
7 purchase totals =	$917.58		$999.9585	$999.96	$999.95	$1,000.00