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	$127.65	12.735%	$143.9062	$143.91	$143.90	$143.90
Purchase #2	$155.78	8.158%	$168.4885	$168.49	$168.50	$168.50
Purchase #3	$195.55	8.298%	$211.7767	$211.78	$211.80	$211.80
Purchase #4	$56.68	4.109%	$59.009	$59.01	$59.00	$59.00
Purchase #5	$85.94	4.672%	$89.9551	$89.96	$89.95	$90.00
Purchase #6	$195.55	6.800%	$208.8474	$208.85	$208.85	$208.80
Purchase #7	$33.41	5.109%	$35.1169	$35.12	$35.10	$35.10
7 purchase totals =	$850.56		$917.0998	$917.12	$917.10	$917.10