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 $220.62   8.159%   $238.6204   $238.62   $238.60   $238.60  
  Purchase #2 $227.41   3.204%   $234.6962   $234.70   $234.70   $234.70  
  Purchase #3 $7.92   8.509%   $8.5939   $8.59   $8.60   $8.60  
  Purchase #4 $23.70   12.183%   $26.5874   $26.59   $26.60   $26.60  
  Purchase #5 $62.95   7.501%   $67.6719   $67.67   $67.65   $67.70  
  Purchase #6 $72.46   4.357%   $75.6171   $75.62   $75.60   $75.60  
  Purchase #7 $205.87   7.292%   $220.882   $220.88   $220.90   $220.90  
  7 purchase totals = $820.93       $872.6689   $872.67   $872.65   $872.70