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	$46.29	12.356%	$52.0096	$52.01	$52.00	$52.00
Purchase #2	$210.82	13.478%	$239.2343	$239.23	$239.25	$239.20
Purchase #3	$196.29	10.698%	$217.2891	$217.29	$217.30	$217.30
Purchase #4	$42.45	7.365%	$45.5764	$45.58	$45.60	$45.60
Purchase #5	$33.67	8.241%	$36.4447	$36.44	$36.45	$36.40
Purchase #6	$106.53	13.195%	$120.5866	$120.59	$120.60	$120.60
Purchase #7	$41.50	4.244%	$43.2613	$43.26	$43.25	$43.30
7 purchase totals =	$677.55		$754.4020	$754.40	$754.45	$754.40