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	$40.58	3.831%	$42.1346	$42.13	$42.15	$42.10
Purchase #2	$36.60	11.660%	$40.8676	$40.87	$40.85	$40.90
Purchase #3	$55.90	11.737%	$62.461	$62.46	$62.45	$62.50
Purchase #4	$33.82	3.448%	$34.9861	$34.99	$35.00	$35.00
Purchase #5	$202.57	6.853%	$216.4521	$216.45	$216.45	$216.50
Purchase #6	$17.37	11.481%	$19.3642	$19.36	$19.35	$19.40
Purchase #7	$68.77	5.714%	$72.6995	$72.70	$72.70	$72.70
7 purchase totals =	$455.61		$488.9651	$488.96	$488.95	$489.10