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 $64.85   10.691%   $71.7831   $71.78   $71.80   $71.80  
  Purchase #2 $179.30   6.737%   $191.3794   $191.38   $191.40   $191.40  
  Purchase #3 $118.93   12.314%   $133.575   $133.58   $133.60   $133.60  
  Purchase #4 $21.81   12.426%   $24.5201   $24.52   $24.50   $24.50  
  Purchase #5 $230.74   7.234%   $247.4317   $247.43   $247.45   $247.40  
  Purchase #6 $60.71   5.142%   $63.8317   $63.83   $63.85   $63.80  
  Purchase #7 $214.60   5.801%   $227.0489   $227.05   $227.05   $227.00  
  7 purchase totals = $890.94       $959.5699   $959.57   $959.65   $959.50