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 $210.44   4.848%   $220.6421   $220.64   $220.65   $220.60  
  Purchase #2 $230.71   13.540%   $261.9481   $261.95   $261.95   $261.90  
  Purchase #3 $83.81   11.234%   $93.2252   $93.23   $93.25   $93.20  
  Purchase #4 $89.54   3.719%   $92.87   $92.87   $92.85   $92.90  
  Purchase #5 $240.65   10.363%   $265.5886   $265.59   $265.60   $265.60  
  Purchase #6 $197.42   9.843%   $216.8521   $216.85   $216.85   $216.90  
  Purchase #7 $113.25   9.832%   $124.3847   $124.38   $124.40   $124.40  
  7 purchase totals = $1,165.82       $1,275.5108   $1,275.51   $1,275.55   $1,275.50