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	$18.98	12.405%	$21.3345	$21.33	$21.35	$21.30
Purchase #2	$80.72	12.604%	$90.8939	$90.89	$90.90	$90.90
Purchase #3	$160.72	8.156%	$173.8283	$173.83	$173.85	$173.80
Purchase #4	$235.27	4.306%	$245.4007	$245.40	$245.40	$245.40
Purchase #5	$250.57	13.324%	$283.9559	$283.96	$283.95	$284.00
Purchase #6	$106.67	9.223%	$116.5082	$116.51	$116.50	$116.50
Purchase #7	$206.31	5.600%	$217.8634	$217.86	$217.85	$217.90
7 purchase totals =	$1,059.24		$1,149.7849	$1,149.78	$1,149.80	$1,149.80