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	$199.99	12.831%	$225.6507	$225.65	$225.65	$225.70
Purchase #2	$40.34	7.774%	$43.476	$43.48	$43.50	$43.50
Purchase #3	$196.62	13.207%	$222.5876	$222.59	$222.60	$222.60
Purchase #4	$153.98	6.710%	$164.3121	$164.31	$164.30	$164.30
Purchase #5	$66.99	8.592%	$72.7458	$72.75	$72.75	$72.70
Purchase #6	$72.57	8.666%	$78.8589	$78.86	$78.85	$78.90
Purchase #7	$11.70	12.808%	$13.1985	$13.20	$13.20	$13.20
7 purchase totals =	$742.19		$820.8296	$820.84	$820.85	$820.90