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	$16.66	10.502%	$18.4096	$18.41	$18.40	$18.40
Purchase #2	$33.93	3.844%	$35.2343	$35.23	$35.25	$35.20
Purchase #3	$89.90	5.770%	$95.0872	$95.09	$95.10	$95.10
Purchase #4	$107.61	13.507%	$122.1449	$122.14	$122.15	$122.10
Purchase #5	$5.81	11.715%	$6.4906	$6.49	$6.50	$6.50
Purchase #6	$81.77	10.856%	$90.647	$90.65	$90.65	$90.60
Purchase #7	$146.46	3.165%	$151.0955	$151.10	$151.10	$151.10
7 purchase totals =	$482.14		$519.1091	$519.11	$519.15	$519.00