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 $204.77   5.774%   $216.5934   $216.59   $216.60   $216.60  
  Purchase #2 $81.34   4.826%   $85.2655   $85.27   $85.25   $85.30  
  Purchase #3 $89.56   6.298%   $95.2005   $95.20   $95.20   $95.20  
  Purchase #4 $241.84   13.488%   $274.4594   $274.46   $274.45   $274.50  
  Purchase #5 $243.86   7.123%   $261.2301   $261.23   $261.25   $261.20  
  Purchase #6 $188.64   5.497%   $199.0095   $199.01   $199.00   $199.00  
  Purchase #7 $128.85   4.303%   $134.3944   $134.39   $134.40   $134.40  
  7 purchase totals = $1,178.86       $1,266.1528   $1,266.15   $1,266.15   $1,266.20