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	$241.68	7.661%	$260.1951	$260.20	$260.20	$260.20
Purchase #2	$204.88	8.854%	$223.0201	$223.02	$223.00	$223.00
Purchase #3	$143.37	11.549%	$159.9278	$159.93	$159.95	$159.90
Purchase #4	$31.63	12.354%	$35.5376	$35.54	$35.55	$35.50
Purchase #5	$70.82	10.822%	$78.4841	$78.48	$78.50	$78.50
Purchase #6	$100.60	10.576%	$111.2395	$111.24	$111.25	$111.20
Purchase #7	$70.39	11.321%	$78.3589	$78.36	$78.35	$78.40
7 purchase totals =	$863.37		$946.7631	$946.77	$946.80	$946.70