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	$109.90	12.259%	$123.3726	$123.37	$123.35	$123.40
Purchase #2	$64.70	10.208%	$71.3046	$71.30	$71.30	$71.30
Purchase #3	$246.90	10.202%	$272.0887	$272.09	$272.10	$272.10
Purchase #4	$93.95	12.676%	$105.8591	$105.86	$105.85	$105.90
Purchase #5	$73.89	11.291%	$82.2329	$82.23	$82.25	$82.20
Purchase #6	$143.29	13.253%	$162.2802	$162.28	$162.30	$162.30
Purchase #7	$246.34	7.719%	$265.355	$265.36	$265.35	$265.40
7 purchase totals =	$978.97		$1,082.4931	$1,082.49	$1,082.50	$1,082.60