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	$29.55	6.236%	$31.3927	$31.39	$31.40	$31.40
Purchase #2	$87.66	4.161%	$91.3075	$91.31	$91.30	$91.30
Purchase #3	$132.56	8.459%	$143.7733	$143.77	$143.75	$143.80
Purchase #4	$12.43	8.619%	$13.5013	$13.50	$13.50	$13.50
Purchase #5	$165.57	4.208%	$172.5372	$172.54	$172.55	$172.50
Purchase #6	$146.77	3.687%	$152.1814	$152.18	$152.20	$152.20
Purchase #7	$189.57	12.722%	$213.6871	$213.69	$213.70	$213.70
7 purchase totals =	$764.11		$818.3805	$818.38	$818.40	$818.40