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 $175.29   12.119%   $196.5334   $196.53   $196.55   $196.50  
  Purchase #2 $194.57   12.342%   $218.5838   $218.58   $218.60   $218.60  
  Purchase #3 $250.28   3.180%   $258.2389   $258.24   $258.25   $258.20  
  Purchase #4 $136.26   7.271%   $146.1675   $146.17   $146.15   $146.20  
  Purchase #5 $11.97   6.352%   $12.7303   $12.73   $12.75   $12.70  
  Purchase #6 $247.44   7.106%   $265.0231   $265.02   $265.00   $265.00  
  Purchase #7 $60.42   5.185%   $63.5528   $63.55   $63.55   $63.60  
  7 purchase totals = $1,076.23       $1,160.8298   $1,160.82   $1,160.85   $1,160.80