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 $80.67   13.634%   $91.6685   $91.67   $91.65   $91.70  
  Purchase #2 $69.75   11.853%   $78.0175   $78.02   $78.00   $78.00  
  Purchase #3 $126.30   12.241%   $141.7604   $141.76   $141.75   $141.80  
  Purchase #4 $97.81   4.733%   $102.4393   $102.44   $102.45   $102.40  
  Purchase #5 $51.85   7.691%   $55.8378   $55.84   $55.85   $55.80  
  Purchase #6 $103.30   13.799%   $117.5544   $117.55   $117.55   $117.60  
  Purchase #7 $239.67   13.777%   $272.6893   $272.69   $272.70   $272.70  
  7 purchase totals = $769.35       $859.9672   $859.97   $859.95   $860.00