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	$82.26	9.600%	$90.157	$90.16	$90.15	$90.20
Purchase #2	$29.89	4.373%	$31.1971	$31.20	$31.20	$31.20
Purchase #3	$169.49	3.867%	$176.0442	$176.04	$176.05	$176.00
Purchase #4	$31.50	7.139%	$33.7488	$33.75	$33.75	$33.70
Purchase #5	$80.50	13.485%	$91.3554	$91.36	$91.35	$91.40
Purchase #6	$87.96	4.290%	$91.7335	$91.73	$91.75	$91.70
Purchase #7	$159.78	3.762%	$165.7909	$165.79	$165.80	$165.80
7 purchase totals =	$641.38		$680.0269	$680.03	$680.05	$680.00