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	$108.81	3.543%	$112.6651	$112.67	$112.65	$112.70
Purchase #2	$136.32	4.430%	$142.359	$142.36	$142.35	$142.40
Purchase #3	$32.54	8.508%	$35.3085	$35.31	$35.30	$35.30
Purchase #4	$113.78	10.574%	$125.8111	$125.81	$125.80	$125.80
Purchase #5	$152.91	9.610%	$167.6047	$167.60	$167.60	$167.60
Purchase #6	$143.47	8.838%	$156.1499	$156.15	$156.15	$156.10
Purchase #7	$86.78	4.664%	$90.8274	$90.83	$90.85	$90.80
7 purchase totals =	$774.61		$830.7257	$830.73	$830.70	$830.70