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 $56.76   12.320%   $63.7528   $63.75   $63.75   $63.80  
  Purchase #2 $245.98   8.445%   $266.753   $266.75   $266.75   $266.80  
  Purchase #3 $166.83   11.267%   $185.6267   $185.63   $185.65   $185.60  
  Purchase #4 $87.94   3.699%   $91.1929   $91.19   $91.20   $91.20  
  Purchase #5 $193.60   11.455%   $215.7769   $215.78   $215.80   $215.80  
  Purchase #6 $126.92   12.646%   $142.9703   $142.97   $142.95   $143.00  
  Purchase #7 $229.28   5.451%   $241.7781   $241.78   $241.80   $241.80  
  7 purchase totals = $1,107.31       $1,207.8507   $1,207.85   $1,207.90   $1,208.00