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	$36.30	10.477%	$40.1032	$40.10	$40.10	$40.10
Purchase #2	$153.38	9.737%	$168.3146	$168.31	$168.30	$168.30
Purchase #3	$48.81	12.148%	$54.7394	$54.74	$54.75	$54.70
Purchase #4	$31.25	5.864%	$33.0825	$33.08	$33.10	$33.10
Purchase #5	$31.34	4.710%	$32.8161	$32.82	$32.80	$32.80
Purchase #6	$243.72	11.603%	$271.9988	$272.00	$272.00	$272.00
Purchase #7	$223.50	8.407%	$242.2896	$242.29	$242.30	$242.30
7 purchase totals =	$768.30		$843.3442	$843.34	$843.35	$843.30