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	$121.57	5.862%	$128.6964	$128.70	$128.70	$128.70
Purchase #2	$177.47	8.650%	$192.8212	$192.82	$192.80	$192.80
Purchase #3	$215.69	11.481%	$240.4534	$240.45	$240.45	$240.50
Purchase #4	$111.43	8.530%	$120.935	$120.94	$120.95	$120.90
Purchase #5	$149.64	10.757%	$165.7368	$165.74	$165.75	$165.70
Purchase #6	$80.45	6.725%	$85.8603	$85.86	$85.85	$85.90
Purchase #7	$61.50	12.228%	$69.0202	$69.02	$69.00	$69.00
7 purchase totals =	$917.75		$1,003.5233	$1,003.53	$1,003.50	$1,003.50