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	$7.56	12.620%	$8.5141	$8.51	$8.50	$8.50
Purchase #2	$18.80	11.194%	$20.9045	$20.90	$20.90	$20.90
Purchase #3	$25.63	3.651%	$26.5658	$26.57	$26.55	$26.60
Purchase #4	$20.83	5.361%	$21.9467	$21.95	$21.95	$21.90
Purchase #5	$90.51	11.494%	$100.9132	$100.91	$100.90	$100.90
Purchase #6	$48.92	6.800%	$52.2466	$52.25	$52.25	$52.20
Purchase #7	$78.91	10.553%	$87.2374	$87.24	$87.25	$87.20
7 purchase totals =	$291.16		$318.3283	$318.33	$318.30	$318.20