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 $146.71   10.403%   $161.9722   $161.97   $161.95   $162.00  
  Purchase #2 $36.97   9.290%   $40.4045   $40.40   $40.40   $40.40  
  Purchase #3 $198.84   7.211%   $213.1784   $213.18   $213.20   $213.20  
  Purchase #4 $52.86   12.430%   $59.4305   $59.43   $59.45   $59.40  
  Purchase #5 $31.82   6.769%   $33.9739   $33.97   $33.95   $34.00  
  Purchase #6 $168.70   6.527%   $179.711   $179.71   $179.70   $179.70  
  Purchase #7 $181.31   6.577%   $193.2348   $193.23   $193.25   $193.20  
  7 purchase totals = $817.21       $881.9053   $881.89   $881.90   $881.90