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	$235.61	12.250%	$264.4722	$264.47	$264.45	$264.50
Purchase #2	$26.68	6.685%	$28.4636	$28.46	$28.45	$28.50
Purchase #3	$86.57	13.296%	$98.0803	$98.08	$98.10	$98.10
Purchase #4	$37.70	8.775%	$41.0082	$41.01	$41.00	$41.00
Purchase #5	$10.42	4.789%	$10.919	$10.92	$10.90	$10.90
Purchase #6	$117.61	11.498%	$131.1328	$131.13	$131.15	$131.10
Purchase #7	$44.65	5.264%	$47.0004	$47.00	$47.00	$47.00
7 purchase totals =	$559.24		$621.0765	$621.07	$621.05	$621.10