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	$243.75	5.239%	$256.5201	$256.52	$256.50	$256.50
Purchase #2	$82.73	12.866%	$93.374	$93.37	$93.35	$93.40
Purchase #3	$39.27	7.600%	$42.2545	$42.25	$42.25	$42.30
Purchase #4	$207.91	9.199%	$227.0356	$227.04	$227.05	$227.00
Purchase #5	$107.52	11.684%	$120.0826	$120.08	$120.10	$120.10
Purchase #6	$148.47	5.816%	$157.105	$157.11	$157.10	$157.10
Purchase #7	$76.76	7.473%	$82.4963	$82.50	$82.50	$82.50
7 purchase totals =	$906.41		$978.8681	$978.87	$978.85	$978.90