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	$35.30	7.311%	$37.8808	$37.88	$37.90	$37.90
Purchase #2	$76.61	9.171%	$83.6359	$83.64	$83.65	$83.60
Purchase #3	$220.27	13.747%	$250.5505	$250.55	$250.55	$250.60
Purchase #4	$75.41	4.327%	$78.673	$78.67	$78.65	$78.70
Purchase #5	$12.38	11.190%	$13.7653	$13.77	$13.75	$13.80
Purchase #6	$180.60	4.741%	$189.1622	$189.16	$189.15	$189.20
Purchase #7	$209.33	10.109%	$230.4912	$230.49	$230.50	$230.50
7 purchase totals =	$809.90		$884.1589	$884.16	$884.15	$884.30