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	$178.33	12.295%	$200.2557	$200.26	$200.25	$200.30
Purchase #2	$110.46	11.594%	$123.2667	$123.27	$123.25	$123.30
Purchase #3	$30.47	6.725%	$32.5191	$32.52	$32.50	$32.50
Purchase #4	$189.42	4.534%	$198.0083	$198.01	$198.00	$198.00
Purchase #5	$135.48	4.379%	$141.4127	$141.41	$141.40	$141.40
Purchase #6	$146.70	3.276%	$151.5059	$151.51	$151.50	$151.50
Purchase #7	$26.84	9.335%	$29.3455	$29.35	$29.35	$29.30
7 purchase totals =	$817.70		$876.3139	$876.33	$876.25	$876.30