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	$11.59	10.306%	$12.7845	$12.78	$12.80	$12.80
Purchase #2	$61.72	6.343%	$65.6349	$65.63	$65.65	$65.60
Purchase #3	$19.61	10.763%	$21.7206	$21.72	$21.70	$21.70
Purchase #4	$132.79	4.302%	$138.5026	$138.50	$138.50	$138.50
Purchase #5	$181.71	9.466%	$198.9107	$198.91	$198.90	$198.90
Purchase #6	$17.47	4.292%	$18.2198	$18.22	$18.20	$18.20
Purchase #7	$192.80	9.165%	$210.4701	$210.47	$210.45	$210.50
7 purchase totals =	$617.69		$666.2432	$666.23	$666.20	$666.20