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	$234.98	13.228%	$266.0632	$266.06	$266.05	$266.10
Purchase #2	$187.62	6.641%	$200.0798	$200.08	$200.10	$200.10
Purchase #3	$193.34	12.127%	$216.7863	$216.79	$216.80	$216.80
Purchase #4	$92.84	8.227%	$100.4779	$100.48	$100.50	$100.50
Purchase #5	$150.73	9.671%	$165.3071	$165.31	$165.30	$165.30
Purchase #6	$71.25	9.188%	$77.7965	$77.80	$77.80	$77.80
Purchase #7	$34.77	11.861%	$38.8941	$38.89	$38.90	$38.90
7 purchase totals =	$965.53		$1,065.4049	$1,065.41	$1,065.45	$1,065.50