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	$222.68	3.690%	$230.8969	$230.90	$230.90	$230.90
Purchase #2	$117.48	11.528%	$131.0231	$131.02	$131.00	$131.00
Purchase #3	$51.61	13.378%	$58.5144	$58.51	$58.50	$58.50
Purchase #4	$44.34	12.441%	$49.8563	$49.86	$49.85	$49.90
Purchase #5	$249.47	10.782%	$276.3679	$276.37	$276.35	$276.40
Purchase #6	$153.46	13.266%	$173.818	$173.82	$173.80	$173.80
Purchase #7	$63.82	13.694%	$72.5595	$72.56	$72.55	$72.60
7 purchase totals =	$902.86		$993.0361	$993.04	$992.95	$993.10