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	$11.91	9.330%	$13.0212	$13.02	$13.00	$13.00
Purchase #2	$135.51	5.620%	$143.1257	$143.13	$143.15	$143.10
Purchase #3	$164.67	12.384%	$185.0627	$185.06	$185.05	$185.10
Purchase #4	$213.84	7.469%	$229.8117	$229.81	$229.80	$229.80
Purchase #5	$37.86	10.799%	$41.9485	$41.95	$41.95	$41.90
Purchase #6	$31.37	11.807%	$35.0739	$35.07	$35.05	$35.10
Purchase #7	$113.41	12.483%	$127.567	$127.57	$127.55	$127.60
7 purchase totals =	$708.57		$775.6107	$775.61	$775.55	$775.60