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 $248.33   13.558%   $281.9986   $282.00   $282.00   $282.00  
  Purchase #2 $231.26   5.151%   $243.1722   $243.17   $243.15   $243.20  
  Purchase #3 $232.26   9.359%   $253.9972   $254.00   $254.00   $254.00  
  Purchase #4 $237.61   10.476%   $262.502   $262.50   $262.50   $262.50  
  Purchase #5 $152.85   7.321%   $164.0401   $164.04   $164.05   $164.00  
  Purchase #6 $64.60   7.134%   $69.2086   $69.21   $69.20   $69.20  
  Purchase #7 $84.72   6.721%   $90.414   $90.41   $90.40   $90.40  
  7 purchase totals = $1,251.63       $1,365.3327   $1,365.33   $1,365.30   $1,365.30