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	$10.67	13.650%	$12.1265	$12.13	$12.15	$12.10
Purchase #2	$194.90	13.760%	$221.7182	$221.72	$221.70	$221.70
Purchase #3	$245.44	10.696%	$271.6923	$271.69	$271.70	$271.70
Purchase #4	$238.48	4.860%	$250.0701	$250.07	$250.05	$250.10
Purchase #5	$104.97	3.296%	$108.4298	$108.43	$108.45	$108.40
Purchase #6	$68.77	5.648%	$72.6541	$72.65	$72.65	$72.70
Purchase #7	$140.81	13.333%	$159.5842	$159.58	$159.60	$159.60
7 purchase totals =	$1,004.04		$1,096.2752	$1,096.27	$1,096.30	$1,096.30