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	$240.83	13.838%	$274.1561	$274.16	$274.15	$274.20
Purchase #2	$11.55	6.443%	$12.2942	$12.29	$12.30	$12.30
Purchase #3	$31.90	5.201%	$33.5591	$33.56	$33.55	$33.60
Purchase #4	$99.58	6.656%	$106.208	$106.21	$106.20	$106.20
Purchase #5	$138.97	4.202%	$144.8095	$144.81	$144.80	$144.80
Purchase #6	$186.39	5.615%	$196.8558	$196.86	$196.85	$196.90
Purchase #7	$68.79	10.853%	$76.2558	$76.26	$76.25	$76.30
7 purchase totals =	$778.01		$844.1385	$844.15	$844.10	$844.30