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	$85.60	6.260%	$90.9586	$90.96	$90.95	$91.00
Purchase #2	$204.93	4.804%	$214.7748	$214.77	$214.75	$214.80
Purchase #3	$59.30	9.676%	$65.0379	$65.04	$65.05	$65.00
Purchase #4	$74.38	8.102%	$80.4063	$80.41	$80.40	$80.40
Purchase #5	$138.91	10.167%	$153.033	$153.03	$153.05	$153.00
Purchase #6	$69.32	12.536%	$78.01	$78.01	$78.00	$78.00
Purchase #7	$109.43	6.294%	$116.3175	$116.32	$116.30	$116.30
7 purchase totals =	$741.87		$798.5381	$798.54	$798.50	$798.50