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	$225.27	13.798%	$256.3528	$256.35	$256.35	$256.40
Purchase #2	$28.38	10.806%	$31.4467	$31.45	$31.45	$31.40
Purchase #3	$201.75	10.413%	$222.7582	$222.76	$222.75	$222.80
Purchase #4	$74.34	11.475%	$82.8705	$82.87	$82.85	$82.90
Purchase #5	$150.35	8.299%	$162.8275	$162.83	$162.85	$162.80
Purchase #6	$196.67	10.715%	$217.7432	$217.74	$217.75	$217.70
Purchase #7	$78.42	4.776%	$82.1653	$82.17	$82.15	$82.20
7 purchase totals =	$955.18		$1,056.1642	$1,056.17	$1,056.15	$1,056.20