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	$138.53	7.173%	$148.4668	$148.47	$148.45	$148.50
Purchase #2	$77.52	6.413%	$82.4914	$82.49	$82.50	$82.50
Purchase #3	$126.48	11.715%	$141.2971	$141.30	$141.30	$141.30
Purchase #4	$203.59	9.105%	$222.1269	$222.13	$222.15	$222.10
Purchase #5	$105.86	6.804%	$113.0627	$113.06	$113.05	$113.10
Purchase #6	$7.52	4.306%	$7.8438	$7.84	$7.85	$7.80
Purchase #7	$125.64	12.511%	$141.3588	$141.36	$141.35	$141.40
7 purchase totals =	$785.14		$856.6475	$856.65	$856.65	$856.70