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	$102.29	6.814%	$109.26	$109.26	$109.25	$109.30
Purchase #2	$49.48	10.658%	$54.7536	$54.75	$54.75	$54.80
Purchase #3	$34.57	6.702%	$36.8869	$36.89	$36.90	$36.90
Purchase #4	$221.65	13.176%	$250.8546	$250.85	$250.85	$250.90
Purchase #5	$199.27	4.773%	$208.7812	$208.78	$208.80	$208.80
Purchase #6	$228.47	11.821%	$255.4774	$255.48	$255.50	$255.50
Purchase #7	$246.50	10.787%	$273.09	$273.09	$273.10	$273.10
7 purchase totals =	$1,082.23		$1,189.1037	$1,189.10	$1,189.15	$1,189.30