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 $211.99   5.294%   $223.2128   $223.21   $223.20   $223.20  
  Purchase #2 $118.37   13.147%   $133.9321   $133.93   $133.95   $133.90  
  Purchase #3 $56.61   13.355%   $64.1703   $64.17   $64.15   $64.20  
  Purchase #4 $123.44   8.304%   $133.6905   $133.69   $133.70   $133.70  
  Purchase #5 $87.31   5.562%   $92.1662   $92.17   $92.15   $92.20  
  Purchase #6 $177.63   11.738%   $198.4802   $198.48   $198.50   $198.50  
  Purchase #7 $57.94   13.589%   $65.8135   $65.81   $65.80   $65.80  
  7 purchase totals = $833.29       $911.4656   $911.46   $911.45   $911.50