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	$139.56	10.273%	$153.897	$153.90	$153.90	$153.90
Purchase #2	$15.44	9.656%	$16.9309	$16.93	$16.95	$16.90
Purchase #3	$169.84	5.122%	$178.5392	$178.54	$178.55	$178.50
Purchase #4	$126.43	12.562%	$142.3121	$142.31	$142.30	$142.30
Purchase #5	$37.89	11.303%	$42.1727	$42.17	$42.15	$42.20
Purchase #6	$12.63	6.704%	$13.4767	$13.48	$13.50	$13.50
Purchase #7	$222.52	4.253%	$231.9838	$231.98	$232.00	$232.00
7 purchase totals =	$724.31		$779.3124	$779.31	$779.35	$779.30