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 $68.68   6.705%   $73.285   $73.29   $73.30   $73.30  
  Purchase #2 $95.60   5.786%   $101.1314   $101.13   $101.15   $101.10  
  Purchase #3 $111.66   12.529%   $125.6499   $125.65   $125.65   $125.60  
  Purchase #4 $80.32   6.840%   $85.8139   $85.81   $85.80   $85.80  
  Purchase #5 $178.44   9.582%   $195.5381   $195.54   $195.55   $195.50  
  Purchase #6 $242.47   8.752%   $263.691   $263.69   $263.70   $263.70  
  Purchase #7 $109.52   5.383%   $115.4155   $115.42   $115.40   $115.40  
  7 purchase totals = $886.69       $960.5248   $960.53   $960.55   $960.40