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	$229.75	3.855%	$238.6069	$238.61	$238.60	$238.60
Purchase #2	$86.68	13.246%	$98.1616	$98.16	$98.15	$98.20
Purchase #3	$111.27	8.122%	$120.3073	$120.31	$120.30	$120.30
Purchase #4	$139.98	12.790%	$157.8834	$157.88	$157.90	$157.90
Purchase #5	$98.41	13.712%	$111.904	$111.90	$111.90	$111.90
Purchase #6	$14.35	5.658%	$15.1619	$15.16	$15.15	$15.20
Purchase #7	$141.48	4.368%	$147.6598	$147.66	$147.65	$147.70
7 purchase totals =	$821.92		$889.6849	$889.68	$889.65	$889.80