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	$80.99	6.692%	$86.4099	$86.41	$86.40	$86.40
Purchase #2	$238.41	13.241%	$269.9779	$269.98	$270.00	$270.00
Purchase #3	$182.43	7.538%	$196.1816	$196.18	$196.20	$196.20
Purchase #4	$130.86	12.191%	$146.8131	$146.81	$146.80	$146.80
Purchase #5	$11.49	6.866%	$12.2789	$12.28	$12.30	$12.30
Purchase #6	$58.78	13.776%	$66.8775	$66.88	$66.90	$66.90
Purchase #7	$10.78	5.202%	$11.3408	$11.34	$11.35	$11.30
7 purchase totals =	$713.74		$789.8797	$789.88	$789.95	$789.90