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	$28.38	6.170%	$30.131	$30.13	$30.15	$30.10
Purchase #2	$35.77	4.841%	$37.5016	$37.50	$37.50	$37.50
Purchase #3	$194.90	6.854%	$208.2584	$208.26	$208.25	$208.30
Purchase #4	$45.64	8.824%	$49.6673	$49.67	$49.65	$49.70
Purchase #5	$55.30	8.184%	$59.8258	$59.83	$59.85	$59.80
Purchase #6	$47.93	11.624%	$53.5014	$53.50	$53.50	$53.50
Purchase #7	$143.45	5.177%	$150.8764	$150.88	$150.90	$150.90
7 purchase totals =	$551.37		$589.7619	$589.77	$589.80	$589.80