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 $56.48   7.249%   $60.5742   $60.57   $60.55   $60.60  
  Purchase #2 $186.67   12.196%   $209.4363   $209.44   $209.45   $209.40  
  Purchase #3 $5.86   9.607%   $6.423   $6.42   $6.40   $6.40  
  Purchase #4 $237.81   6.544%   $253.3723   $253.37   $253.35   $253.40  
  Purchase #5 $162.39   10.593%   $179.592   $179.59   $179.60   $179.60  
  Purchase #6 $24.78   10.601%   $27.4069   $27.41   $27.40   $27.40  
  Purchase #7 $130.77   4.291%   $136.3813   $136.38   $136.40   $136.40  
  7 purchase totals = $804.76       $873.1860   $873.18   $873.15   $873.20