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	$239.83	13.676%	$272.6292	$272.63	$272.65	$272.60
Purchase #2	$10.57	9.656%	$11.5906	$11.59	$11.60	$11.60
Purchase #3	$98.70	8.318%	$106.9099	$106.91	$106.90	$106.90
Purchase #4	$29.72	11.610%	$33.1705	$33.17	$33.15	$33.20
Purchase #5	$157.48	5.112%	$165.5304	$165.53	$165.55	$165.50
Purchase #6	$217.84	13.493%	$247.2332	$247.23	$247.25	$247.20
Purchase #7	$109.94	12.630%	$123.8254	$123.83	$123.85	$123.80
7 purchase totals =	$864.08		$960.8892	$960.89	$960.95	$960.80