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	$210.59	13.674%	$239.3861	$239.39	$239.40	$239.40
Purchase #2	$35.97	12.425%	$40.4393	$40.44	$40.45	$40.40
Purchase #3	$48.61	13.120%	$54.9876	$54.99	$55.00	$55.00
Purchase #4	$104.83	4.711%	$109.7685	$109.77	$109.75	$109.80
Purchase #5	$228.50	12.851%	$257.8645	$257.86	$257.85	$257.90
Purchase #6	$35.47	12.653%	$39.958	$39.96	$39.95	$40.00
Purchase #7	$86.44	4.134%	$90.0134	$90.01	$90.00	$90.00
7 purchase totals =	$750.41		$832.4174	$832.42	$832.40	$832.50