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 $62.96   5.803%   $66.6136   $66.61   $66.60   $66.60  
  Purchase #2 $41.86   6.537%   $44.5964   $44.60   $44.60   $44.60  
  Purchase #3 $143.72   8.378%   $155.7609   $155.76   $155.75   $155.80  
  Purchase #4 $149.43   5.660%   $157.8877   $157.89   $157.90   $157.90  
  Purchase #5 $112.96   4.443%   $117.9788   $117.98   $118.00   $118.00  
  Purchase #6 $122.80   8.864%   $133.685   $133.69   $133.70   $133.70  
  Purchase #7 $188.56   3.645%   $195.433   $195.43   $195.45   $195.40  
  7 purchase totals = $822.29       $871.9554   $871.96   $872.00   $872.00