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 $186.96   6.255%   $198.6543   $198.65   $198.65   $198.70  
  Purchase #2 $163.50   8.186%   $176.8841   $176.88   $176.90   $176.90  
  Purchase #3 $245.96   4.633%   $257.3553   $257.36   $257.35   $257.40  
  Purchase #4 $73.61   7.276%   $78.9659   $78.97   $78.95   $79.00  
  Purchase #5 $238.61   7.762%   $257.1309   $257.13   $257.15   $257.10  
  Purchase #6 $62.31   13.440%   $70.6845   $70.68   $70.70   $70.70  
  Purchase #7 $152.56   5.786%   $161.3871   $161.39   $161.40   $161.40  
  7 purchase totals = $1,123.51       $1,201.0621   $1,201.06   $1,201.10   $1,201.20