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	$6.43	4.703%	$6.7324	$6.73	$6.75	$6.70
Purchase #2	$167.75	10.830%	$185.9173	$185.92	$185.90	$185.90
Purchase #3	$48.25	8.405%	$52.3054	$52.31	$52.30	$52.30
Purchase #4	$92.83	11.326%	$103.3439	$103.34	$103.35	$103.30
Purchase #5	$28.38	13.357%	$32.1707	$32.17	$32.15	$32.20
Purchase #6	$123.94	10.847%	$137.3838	$137.38	$137.40	$137.40
Purchase #7	$143.92	12.323%	$161.6553	$161.66	$161.65	$161.70
7 purchase totals =	$611.50		$679.5088	$679.51	$679.50	$679.50