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 $191.38   6.641%   $204.0895   $204.09   $204.10   $204.10  
  Purchase #2 $135.84   5.445%   $143.2365   $143.24   $143.25   $143.20  
  Purchase #3 $219.29   3.789%   $227.5989   $227.60   $227.60   $227.60  
  Purchase #4 $56.77   13.306%   $64.3238   $64.32   $64.30   $64.30  
  Purchase #5 $115.62   4.724%   $121.0819   $121.08   $121.10   $121.10  
  Purchase #6 $146.69   11.206%   $163.1281   $163.13   $163.15   $163.10  
  Purchase #7 $26.66   7.221%   $28.5851   $28.59   $28.60   $28.60  
  7 purchase totals = $892.25       $952.0438   $952.05   $952.10   $952.00