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 $59.58   8.620%   $64.7158   $64.72   $64.70   $64.70  
  Purchase #2 $149.99   5.435%   $158.142   $158.14   $158.15   $158.10  
  Purchase #3 $105.30   6.509%   $112.154   $112.15   $112.15   $112.20  
  Purchase #4 $239.47   11.538%   $267.1   $267.10   $267.10   $267.10  
  Purchase #5 $234.55   4.427%   $244.9335   $244.93   $244.95   $244.90  
  Purchase #6 $111.63   13.287%   $126.4623   $126.46   $126.45   $126.50  
  Purchase #7 $8.54   13.123%   $9.6607   $9.66   $9.65   $9.70  
  7 purchase totals = $909.06       $983.1683   $983.16   $983.15   $983.20