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 $119.81   10.378%   $132.2439   $132.24   $132.25   $132.20  
  Purchase #2 $14.91   10.162%   $16.4252   $16.43   $16.45   $16.40  
  Purchase #3 $95.55   6.271%   $101.5419   $101.54   $101.55   $101.50  
  Purchase #4 $148.32   11.214%   $164.9526   $164.95   $164.95   $165.00  
  Purchase #5 $122.56   10.661%   $135.6261   $135.63   $135.65   $135.60  
  Purchase #6 $142.99   4.637%   $149.6204   $149.62   $149.60   $149.60  
  Purchase #7 $166.78   9.119%   $181.9887   $181.99   $182.00   $182.00  
  7 purchase totals = $810.92       $882.3988   $882.40   $882.45   $882.30