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	$208.47	7.648%	$224.4138	$224.41	$224.40	$224.40
Purchase #2	$209.55	3.829%	$217.5737	$217.57	$217.55	$217.60
Purchase #3	$163.49	13.454%	$185.4859	$185.49	$185.50	$185.50
Purchase #4	$22.49	10.683%	$24.8926	$24.89	$24.90	$24.90
Purchase #5	$224.41	11.805%	$250.9016	$250.90	$250.90	$250.90
Purchase #6	$66.80	7.847%	$72.0418	$72.04	$72.05	$72.00
Purchase #7	$224.89	11.162%	$249.9922	$249.99	$250.00	$250.00
7 purchase totals =	$1,120.10		$1,225.3016	$1,225.29	$1,225.30	$1,225.30