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	$66.54	12.130%	$74.6113	$74.61	$74.60	$74.60
Purchase #2	$170.33	11.277%	$189.5381	$189.54	$189.55	$189.50
Purchase #3	$78.43	4.121%	$81.6621	$81.66	$81.65	$81.70
Purchase #4	$218.65	13.398%	$247.9447	$247.94	$247.95	$247.90
Purchase #5	$59.97	12.707%	$67.5904	$67.59	$67.60	$67.60
Purchase #6	$87.74	5.437%	$92.5104	$92.51	$92.50	$92.50
Purchase #7	$44.31	4.712%	$46.3979	$46.40	$46.40	$46.40
7 purchase totals =	$725.97		$800.2549	$800.25	$800.25	$800.20