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 $87.55   7.732%   $94.3194   $94.32   $94.30   $94.30  
  Purchase #2 $130.26   8.744%   $141.6499   $141.65   $141.65   $141.60  
  Purchase #3 $6.39   3.421%   $6.6086   $6.61   $6.60   $6.60  
  Purchase #4 $56.75   8.665%   $61.6674   $61.67   $61.65   $61.70  
  Purchase #5 $154.70   4.509%   $161.6754   $161.68   $161.70   $161.70  
  Purchase #6 $213.27   5.332%   $224.6416   $224.64   $224.65   $224.60  
  Purchase #7 $59.38   4.806%   $62.2338   $62.23   $62.25   $62.20  
  7 purchase totals = $708.30       $752.7961   $752.80   $752.80   $752.70