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	$37.96	4.387%	$39.6253	$39.63	$39.65	$39.60
Purchase #2	$185.92	10.239%	$204.9563	$204.96	$204.95	$205.00
Purchase #3	$9.95	9.507%	$10.8959	$10.90	$10.90	$10.90
Purchase #4	$238.89	11.725%	$266.8999	$266.90	$266.90	$266.90
Purchase #5	$88.81	6.466%	$94.5525	$94.55	$94.55	$94.60
Purchase #6	$72.25	11.734%	$80.7278	$80.73	$80.75	$80.70
Purchase #7	$141.78	4.306%	$147.885	$147.89	$147.90	$147.90
7 purchase totals =	$775.56		$845.5427	$845.56	$845.60	$845.60