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	$103.94	11.441%	$115.8318	$115.83	$115.85	$115.80
Purchase #2	$93.75	12.356%	$105.3338	$105.33	$105.35	$105.30
Purchase #3	$223.97	4.635%	$234.351	$234.35	$234.35	$234.40
Purchase #4	$141.71	10.345%	$156.3699	$156.37	$156.35	$156.40
Purchase #5	$92.70	8.833%	$100.8882	$100.89	$100.90	$100.90
Purchase #6	$179.97	5.868%	$190.5306	$190.53	$190.55	$190.50
Purchase #7	$32.98	7.605%	$35.4881	$35.49	$35.50	$35.50
7 purchase totals =	$869.02		$938.7934	$938.79	$938.85	$938.80