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	$123.95	8.419%	$134.3854	$134.39	$134.40	$134.40
Purchase #2	$111.88	6.143%	$118.7528	$118.75	$118.75	$118.80
Purchase #3	$36.77	9.772%	$40.3632	$40.36	$40.35	$40.40
Purchase #4	$92.81	7.714%	$99.9694	$99.97	$99.95	$100.00
Purchase #5	$156.69	7.606%	$168.6078	$168.61	$168.60	$168.60
Purchase #6	$188.51	6.314%	$200.4125	$200.41	$200.40	$200.40
Purchase #7	$18.78	11.704%	$20.978	$20.98	$21.00	$21.00
7 purchase totals =	$729.39		$783.4691	$783.47	$783.45	$783.60