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	$38.32	10.557%	$42.3654	$42.37	$42.35	$42.40
Purchase #2	$81.48	12.730%	$91.8524	$91.85	$91.85	$91.90
Purchase #3	$73.75	6.453%	$78.5091	$78.51	$78.50	$78.50
Purchase #4	$204.34	9.733%	$224.2284	$224.23	$224.25	$224.20
Purchase #5	$36.39	5.665%	$38.4515	$38.45	$38.45	$38.50
Purchase #6	$47.62	9.766%	$52.2706	$52.27	$52.25	$52.30
Purchase #7	$174.63	8.709%	$189.8385	$189.84	$189.85	$189.80
7 purchase totals =	$656.53		$717.5159	$717.52	$717.50	$717.60