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	$44.33	7.670%	$47.7301	$47.73	$47.75	$47.70
Purchase #2	$37.51	12.694%	$42.2715	$42.27	$42.25	$42.30
Purchase #3	$143.51	9.140%	$156.6268	$156.63	$156.65	$156.60
Purchase #4	$45.39	5.316%	$47.8029	$47.80	$47.80	$47.80
Purchase #5	$81.84	8.505%	$88.8005	$88.80	$88.80	$88.80
Purchase #6	$204.60	8.667%	$222.3327	$222.33	$222.35	$222.30
Purchase #7	$139.64	11.657%	$155.9178	$155.92	$155.90	$155.90
7 purchase totals =	$696.82		$761.4823	$761.48	$761.50	$761.40