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	$169.45	12.345%	$190.3686	$190.37	$190.35	$190.40
Purchase #2	$39.94	10.816%	$44.2599	$44.26	$44.25	$44.30
Purchase #3	$235.33	13.375%	$266.8054	$266.81	$266.80	$266.80
Purchase #4	$81.95	5.138%	$86.1606	$86.16	$86.15	$86.20
Purchase #5	$163.51	3.611%	$169.4143	$169.41	$169.40	$169.40
Purchase #6	$92.82	11.800%	$103.7728	$103.77	$103.75	$103.80
Purchase #7	$72.53	7.585%	$78.0314	$78.03	$78.05	$78.00
7 purchase totals =	$855.53		$938.8130	$938.81	$938.75	$938.90