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	$246.38	3.724%	$255.5552	$255.56	$255.55	$255.60
Purchase #2	$167.54	9.694%	$183.7813	$183.78	$183.80	$183.80
Purchase #3	$76.60	9.431%	$83.8241	$83.82	$83.80	$83.80
Purchase #4	$54.67	8.400%	$59.2623	$59.26	$59.25	$59.30
Purchase #5	$156.80	11.634%	$175.0421	$175.04	$175.05	$175.00
Purchase #6	$50.72	9.558%	$55.5678	$55.57	$55.55	$55.60
Purchase #7	$104.80	13.728%	$119.1869	$119.19	$119.20	$119.20
7 purchase totals =	$857.51		$932.2197	$932.22	$932.20	$932.30