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	$129.75	12.340%	$145.7612	$145.76	$145.75	$145.80
Purchase #2	$107.84	5.584%	$113.8618	$113.86	$113.85	$113.90
Purchase #3	$123.52	13.112%	$139.7159	$139.72	$139.70	$139.70
Purchase #4	$214.93	12.817%	$242.4776	$242.48	$242.50	$242.50
Purchase #5	$20.37	6.439%	$21.6816	$21.68	$21.70	$21.70
Purchase #6	$189.32	10.663%	$209.5072	$209.51	$209.50	$209.50
Purchase #7	$77.56	6.369%	$82.4998	$82.50	$82.50	$82.50
7 purchase totals =	$863.29		$955.5051	$955.51	$955.50	$955.60