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 $61.38   5.420%   $64.7068   $64.71   $64.70   $64.70  
  Purchase #2 $162.47   11.212%   $180.6861   $180.69   $180.70   $180.70  
  Purchase #3 $124.36   11.691%   $138.8989   $138.90   $138.90   $138.90  
  Purchase #4 $59.40   3.794%   $61.6536   $61.65   $61.65   $61.70  
  Purchase #5 $102.75   9.225%   $112.2287   $112.23   $112.25   $112.20  
  Purchase #6 $140.25   6.806%   $149.7954   $149.80   $149.80   $149.80  
  Purchase #7 $49.37   5.715%   $52.1915   $52.19   $52.20   $52.20  
  7 purchase totals = $699.98       $760.1610   $760.17   $760.20   $760.20