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	$99.43	11.544%	$110.9082	$110.91	$110.90	$110.90
Purchase #2	$81.77	13.191%	$92.5563	$92.56	$92.55	$92.60
Purchase #3	$112.35	9.582%	$123.1154	$123.12	$123.10	$123.10
Purchase #4	$33.59	5.867%	$35.5607	$35.56	$35.55	$35.60
Purchase #5	$186.86	12.598%	$210.4006	$210.40	$210.40	$210.40
Purchase #6	$80.34	13.325%	$91.0453	$91.05	$91.05	$91.00
Purchase #7	$74.37	6.108%	$78.9125	$78.91	$78.90	$78.90
7 purchase totals =	$668.71		$742.4990	$742.51	$742.45	$742.50