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 $79.55   8.134%   $86.0206   $86.02   $86.00   $86.00  
  Purchase #2 $125.35   12.352%   $140.8332   $140.83   $140.85   $140.80  
  Purchase #3 $101.74   7.703%   $109.577   $109.58   $109.60   $109.60  
  Purchase #4 $124.99   13.732%   $142.1536   $142.15   $142.15   $142.20  
  Purchase #5 $198.54   9.314%   $217.032   $217.03   $217.05   $217.00  
  Purchase #6 $195.93   12.874%   $221.154   $221.15   $221.15   $221.20  
  Purchase #7 $74.92   5.377%   $78.9484   $78.95   $78.95   $78.90  
  7 purchase totals = $901.02       $995.7188   $995.71   $995.75   $995.70