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 $61.35   10.396%   $67.7279   $67.73   $67.75   $67.70  
  Purchase #2 $218.25   11.192%   $242.6765   $242.68   $242.70   $242.70  
  Purchase #3 $236.47   12.627%   $266.3291   $266.33   $266.35   $266.30  
  Purchase #4 $51.32   12.421%   $57.6945   $57.69   $57.70   $57.70  
  Purchase #5 $81.81   5.417%   $86.2416   $86.24   $86.25   $86.20  
  Purchase #6 $151.52   7.447%   $162.8037   $162.80   $162.80   $162.80  
  Purchase #7 $62.81   7.761%   $67.6847   $67.68   $67.70   $67.70  
  7 purchase totals = $863.53       $951.1580   $951.15   $951.25   $951.10