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 $250.95   10.368%   $276.9685   $276.97   $276.95   $277.00  
  Purchase #2 $182.82   4.272%   $190.6301   $190.63   $190.65   $190.60  
  Purchase #3 $65.53   6.812%   $69.9939   $69.99   $70.00   $70.00  
  Purchase #4 $235.81   6.859%   $251.9842   $251.98   $252.00   $252.00  
  Purchase #5 $200.43   13.707%   $227.9029   $227.90   $227.90   $227.90  
  Purchase #6 $189.64   10.827%   $210.1723   $210.17   $210.15   $210.20  
  Purchase #7 $113.91   9.685%   $124.9422   $124.94   $124.95   $124.90  
  7 purchase totals = $1,239.09       $1,352.5941   $1,352.58   $1,352.60   $1,352.60