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	$240.50	13.653%	$273.3355	$273.34	$273.35	$273.30
Purchase #2	$114.71	7.647%	$123.4819	$123.48	$123.50	$123.50
Purchase #3	$228.94	11.478%	$255.2177	$255.22	$255.20	$255.20
Purchase #4	$31.94	11.495%	$35.6115	$35.61	$35.60	$35.60
Purchase #5	$49.89	6.550%	$53.1578	$53.16	$53.15	$53.20
Purchase #6	$142.28	11.864%	$159.1601	$159.16	$159.15	$159.20
Purchase #7	$18.95	5.319%	$19.958	$19.96	$19.95	$20.00
7 purchase totals =	$827.21		$919.9225	$919.93	$919.90	$920.00