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	$87.44	3.614%	$90.6001	$90.60	$90.60	$90.60
Purchase #2	$25.68	6.428%	$27.3307	$27.33	$27.35	$27.30
Purchase #3	$6.95	7.827%	$7.494	$7.49	$7.50	$7.50
Purchase #4	$131.63	12.823%	$148.5089	$148.51	$148.50	$148.50
Purchase #5	$40.47	7.132%	$43.3563	$43.36	$43.35	$43.40
Purchase #6	$43.84	11.569%	$48.9118	$48.91	$48.90	$48.90
Purchase #7	$126.63	13.690%	$143.9656	$143.97	$143.95	$144.00
7 purchase totals =	$462.64		$510.1674	$510.17	$510.15	$510.20