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 $54.65   12.384%   $61.4179   $61.42   $61.40   $61.40  
  Purchase #2 $218.59   12.368%   $245.6252   $245.63   $245.65   $245.60  
  Purchase #3 $242.88   3.189%   $250.6254   $250.63   $250.65   $250.60  
  Purchase #4 $58.83   6.610%   $62.7187   $62.72   $62.70   $62.70  
  Purchase #5 $88.54   8.414%   $95.9898   $95.99   $96.00   $96.00  
  Purchase #6 $107.77   12.836%   $121.6034   $121.60   $121.60   $121.60  
  Purchase #7 $162.61   7.295%   $174.4724   $174.47   $174.45   $174.50  
  7 purchase totals = $933.87       $1,012.4528   $1,012.46   $1,012.45   $1,012.40