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 $67.73   7.541%   $72.8375   $72.84   $72.85   $72.80  
  Purchase #2 $210.77   4.658%   $220.5877   $220.59   $220.60   $220.60  
  Purchase #3 $212.93   5.149%   $223.8938   $223.89   $223.90   $223.90  
  Purchase #4 $86.83   6.430%   $92.4132   $92.41   $92.40   $92.40  
  Purchase #5 $122.95   11.271%   $136.8077   $136.81   $136.80   $136.80  
  Purchase #6 $14.90   5.302%   $15.69   $15.69   $15.70   $15.70  
  Purchase #7 $74.70   13.197%   $84.5582   $84.56   $84.55   $84.60  
  7 purchase totals = $790.81       $846.7881   $846.79   $846.80   $846.80