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 $23.63   12.498%   $26.5833   $26.58   $26.60   $26.60  
  Purchase #2 $113.60   11.498%   $126.6617   $126.66   $126.65   $126.70  
  Purchase #3 $40.42   5.487%   $42.6378   $42.64   $42.65   $42.60  
  Purchase #4 $145.71   10.785%   $161.4248   $161.42   $161.40   $161.40  
  Purchase #5 $241.98   5.629%   $255.6011   $255.60   $255.60   $255.60  
  Purchase #6 $207.85   11.746%   $232.2641   $232.26   $232.25   $232.30  
  Purchase #7 $203.84   3.110%   $210.1794   $210.18   $210.20   $210.20  
  7 purchase totals = $977.03       $1,055.3522   $1,055.34   $1,055.35   $1,055.40