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 $64.48   13.440%   $73.1461   $73.15   $73.15   $73.10  
  Purchase #2 $10.55   5.612%   $11.1421   $11.14   $11.15   $11.10  
  Purchase #3 $65.89   11.866%   $73.7085   $73.71   $73.70   $73.70  
  Purchase #4 $226.69   6.727%   $241.9394   $241.94   $241.95   $241.90  
  Purchase #5 $69.76   5.684%   $73.7252   $73.73   $73.75   $73.70  
  Purchase #6 $162.35   10.604%   $179.5656   $179.57   $179.55   $179.60  
  Purchase #7 $161.52   6.448%   $171.9348   $171.93   $171.95   $171.90  
  7 purchase totals = $761.24       $825.1617   $825.17   $825.20   $825.00