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	$53.53	3.841%	$55.5861	$55.59	$55.60	$55.60
Purchase #2	$208.48	13.646%	$236.9292	$236.93	$236.95	$236.90
Purchase #3	$98.97	4.844%	$103.7641	$103.76	$103.75	$103.80
Purchase #4	$98.33	4.748%	$102.9987	$103.00	$103.00	$103.00
Purchase #5	$48.34	5.131%	$50.8203	$50.82	$50.80	$50.80
Purchase #6	$52.92	6.678%	$56.454	$56.45	$56.45	$56.50
Purchase #7	$203.37	11.829%	$227.4266	$227.43	$227.45	$227.40
7 purchase totals =	$763.94		$833.9790	$833.98	$834.00	$834.00