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 $242.62   9.614%   $265.9455   $265.95   $265.95   $265.90  
  Purchase #2 $113.65   7.687%   $122.3863   $122.39   $122.40   $122.40  
  Purchase #3 $75.64   6.755%   $80.7495   $80.75   $80.75   $80.70  
  Purchase #4 $28.98   5.437%   $30.5556   $30.56   $30.55   $30.60  
  Purchase #5 $66.60   4.822%   $69.8115   $69.81   $69.80   $69.80  
  Purchase #6 $202.63   12.341%   $227.6366   $227.64   $227.65   $227.60  
  Purchase #7 $46.92   4.465%   $49.015   $49.02   $49.00   $49.00  
  7 purchase totals = $777.04       $846.1000   $846.12   $846.10   $846.00