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	$28.34	11.399%	$31.5705	$31.57	$31.55	$31.60
Purchase #2	$27.92	3.691%	$28.9505	$28.95	$28.95	$29.00
Purchase #3	$116.30	12.660%	$131.0236	$131.02	$131.00	$131.00
Purchase #4	$168.78	13.399%	$191.3948	$191.39	$191.40	$191.40
Purchase #5	$238.80	3.243%	$246.5443	$246.54	$246.55	$246.50
Purchase #6	$135.82	10.535%	$150.1286	$150.13	$150.15	$150.10
Purchase #7	$22.46	4.481%	$23.4664	$23.47	$23.45	$23.50
7 purchase totals =	$738.42		$803.0787	$803.07	$803.05	$803.10