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 $23.81   10.601%   $26.3341   $26.33   $26.35   $26.30  
  Purchase #2 $246.98   11.518%   $275.4272   $275.43   $275.45   $275.40  
  Purchase #3 $67.60   3.585%   $70.0235   $70.02   $70.00   $70.00  
  Purchase #4 $122.50   3.532%   $126.8267   $126.83   $126.85   $126.80  
  Purchase #5 $45.66   13.672%   $51.9026   $51.90   $51.90   $51.90  
  Purchase #6 $222.39   11.379%   $247.6958   $247.70   $247.70   $247.70  
  Purchase #7 $15.68   12.758%   $17.6805   $17.68   $17.70   $17.70  
  7 purchase totals = $744.62       $815.8904   $815.89   $815.95   $815.80