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	$158.86	9.207%	$173.4862	$173.49	$173.50	$173.50
Purchase #2	$44.78	12.523%	$50.3878	$50.39	$50.40	$50.40
Purchase #3	$34.48	12.853%	$38.9117	$38.91	$38.90	$38.90
Purchase #4	$171.69	10.334%	$189.4324	$189.43	$189.45	$189.40
Purchase #5	$151.48	9.527%	$165.9115	$165.91	$165.90	$165.90
Purchase #6	$216.46	8.217%	$234.2465	$234.25	$234.25	$234.20
Purchase #7	$156.64	6.543%	$166.889	$166.89	$166.90	$166.90
7 purchase totals =	$934.39		$1,019.2651	$1,019.27	$1,019.30	$1,019.20