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 $224.37   11.484%   $250.1367   $250.14   $250.15   $250.10  
  Purchase #2 $106.63   8.489%   $115.6818   $115.68   $115.70   $115.70  
  Purchase #3 $173.79   4.663%   $181.8938   $181.89   $181.90   $181.90  
  Purchase #4 $179.57   10.630%   $198.6583   $198.66   $198.65   $198.70  
  Purchase #5 $106.31   11.590%   $118.6313   $118.63   $118.65   $118.60  
  Purchase #6 $153.95   10.403%   $169.9654   $169.97   $169.95   $170.00  
  Purchase #7 $122.58   7.685%   $132.0003   $132.00   $132.00   $132.00  
  7 purchase totals = $1,067.20       $1,166.9676   $1,166.97   $1,167.00   $1,167.00