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	$115.47	6.849%	$123.3785	$123.38	$123.40	$123.40
Purchase #2	$26.34	9.162%	$28.7533	$28.75	$28.75	$28.80
Purchase #3	$95.38	10.550%	$105.4426	$105.44	$105.45	$105.40
Purchase #4	$215.98	3.590%	$223.7337	$223.73	$223.75	$223.70
Purchase #5	$30.71	10.342%	$33.886	$33.89	$33.90	$33.90
Purchase #6	$111.34	4.781%	$116.6632	$116.66	$116.65	$116.70
Purchase #7	$132.71	5.570%	$140.1019	$140.10	$140.10	$140.10
7 purchase totals =	$727.93		$771.9592	$771.95	$772.00	$772.00