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 $52.67   5.484%   $55.5584   $55.56   $55.55   $55.60  
  Purchase #2 $180.92   12.264%   $203.108   $203.11   $203.10   $203.10  
  Purchase #3 $33.49   5.545%   $35.347   $35.35   $35.35   $35.30  
  Purchase #4 $201.27   11.675%   $224.7683   $224.77   $224.75   $224.80  
  Purchase #5 $80.63   5.869%   $85.3622   $85.36   $85.35   $85.40  
  Purchase #6 $145.85   5.704%   $154.1693   $154.17   $154.15   $154.20  
  Purchase #7 $170.71   11.641%   $190.5824   $190.58   $190.60   $190.60  
  7 purchase totals = $865.54       $948.8956   $948.90   $948.85   $949.00