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 $213.46   13.164%   $241.5599   $241.56   $241.55   $241.60  
  Purchase #2 $103.37   9.835%   $113.5364   $113.54   $113.55   $113.50  
  Purchase #3 $125.46   6.303%   $133.3677   $133.37   $133.35   $133.40  
  Purchase #4 $94.42   13.817%   $107.466   $107.47   $107.45   $107.50  
  Purchase #5 $136.57   5.635%   $144.2657   $144.27   $144.25   $144.30  
  Purchase #6 $7.59   12.540%   $8.5418   $8.54   $8.55   $8.50  
  Purchase #7 $127.56   5.250%   $134.2569   $134.26   $134.25   $134.30  
  7 purchase totals = $808.43       $882.9944   $883.01   $882.95   $883.10