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 $236.53   13.588%   $268.6697   $268.67   $268.65   $268.70  
  Purchase #2 $77.74   12.319%   $87.3168   $87.32   $87.30   $87.30  
  Purchase #3 $219.36   13.787%   $249.6032   $249.60   $249.60   $249.60  
  Purchase #4 $146.72   12.206%   $164.6286   $164.63   $164.65   $164.60  
  Purchase #5 $154.41   6.647%   $164.6736   $164.67   $164.65   $164.70  
  Purchase #6 $196.93   5.790%   $208.3322   $208.33   $208.35   $208.30  
  Purchase #7 $102.49   10.525%   $113.2771   $113.28   $113.30   $113.30  
  7 purchase totals = $1,134.18       $1,256.5012   $1,256.50   $1,256.50   $1,256.50