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 $24.73   5.647%   $26.1265   $26.13   $26.15   $26.10  
  Purchase #2 $101.68   9.332%   $111.1688   $111.17   $111.15   $111.20  
  Purchase #3 $58.47   3.490%   $60.5106   $60.51   $60.50   $60.50  
  Purchase #4 $136.40   13.254%   $154.4785   $154.48   $154.50   $154.50  
  Purchase #5 $179.95   8.418%   $195.0982   $195.10   $195.10   $195.10  
  Purchase #6 $190.84   5.650%   $201.6225   $201.62   $201.60   $201.60  
  Purchase #7 $133.68   6.323%   $142.1326   $142.13   $142.15   $142.10  
  7 purchase totals = $825.75       $891.1377   $891.14   $891.15   $891.10