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 $239.48   9.433%   $262.0701   $262.07   $262.05   $262.10  
  Purchase #2 $160.98   6.783%   $171.8993   $171.90   $171.90   $171.90  
  Purchase #3 $13.87   9.193%   $15.1451   $15.15   $15.15   $15.10  
  Purchase #4 $83.80   10.588%   $92.6727   $92.67   $92.65   $92.70  
  Purchase #5 $164.89   5.330%   $173.6786   $173.68   $173.70   $173.70  
  Purchase #6 $250.59   12.726%   $282.4801   $282.48   $282.50   $282.50  
  Purchase #7 $227.77   11.150%   $253.1664   $253.17   $253.15   $253.20  
  7 purchase totals = $1,141.38       $1,251.1123   $1,251.12   $1,251.10   $1,251.20