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	$112.59	6.249%	$119.6257	$119.63	$119.65	$119.60
Purchase #2	$28.95	10.849%	$32.0908	$32.09	$32.10	$32.10
Purchase #3	$107.85	8.154%	$116.6441	$116.64	$116.65	$116.60
Purchase #4	$221.89	10.427%	$245.0265	$245.03	$245.05	$245.00
Purchase #5	$33.48	12.423%	$37.6392	$37.64	$37.65	$37.60
Purchase #6	$51.77	11.265%	$57.6019	$57.60	$57.60	$57.60
Purchase #7	$36.66	9.454%	$40.1258	$40.13	$40.15	$40.10
7 purchase totals =	$593.19		$648.7540	$648.76	$648.85	$648.60