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	$44.68	6.395%	$47.5373	$47.54	$47.55	$47.50
Purchase #2	$40.73	4.862%	$42.7103	$42.71	$42.70	$42.70
Purchase #3	$48.55	5.626%	$51.2814	$51.28	$51.30	$51.30
Purchase #4	$196.76	9.413%	$215.281	$215.28	$215.30	$215.30
Purchase #5	$123.61	10.840%	$137.0093	$137.01	$137.00	$137.00
Purchase #6	$115.59	11.108%	$128.4297	$128.43	$128.45	$128.40
Purchase #7	$49.35	13.362%	$55.9441	$55.94	$55.95	$55.90
7 purchase totals =	$619.27		$678.1931	$678.19	$678.25	$678.10