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 $78.46   8.663%   $85.257   $85.26   $85.25   $85.30  
  Purchase #2 $104.96   8.443%   $113.8218   $113.82   $113.80   $113.80  
  Purchase #3 $206.50   8.867%   $224.8104   $224.81   $224.80   $224.80  
  Purchase #4 $12.44   8.544%   $13.5029   $13.50   $13.50   $13.50  
  Purchase #5 $54.42   8.213%   $58.8895   $58.89   $58.90   $58.90  
  Purchase #6 $9.43   5.412%   $9.9404   $9.94   $9.95   $9.90  
  Purchase #7 $111.96   13.260%   $126.8059   $126.81   $126.80   $126.80  
  7 purchase totals = $578.17       $633.0279   $633.03   $633.00   $633.00