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 $68.79   12.323%   $77.267   $77.27   $77.25   $77.30  
  Purchase #2 $82.72   13.854%   $94.18   $94.18   $94.20   $94.20  
  Purchase #3 $159.68   4.135%   $166.2828   $166.28   $166.30   $166.30  
  Purchase #4 $32.57   5.762%   $34.4467   $34.45   $34.45   $34.40  
  Purchase #5 $57.66   4.523%   $60.268   $60.27   $60.25   $60.30  
  Purchase #6 $154.95   5.165%   $162.9532   $162.95   $162.95   $163.00  
  Purchase #7 $141.44   5.179%   $148.7652   $148.77   $148.75   $148.80  
  7 purchase totals = $697.81       $744.1629   $744.17   $744.15   $744.30