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 $184.97   9.113%   $201.8263   $201.83   $201.85   $201.80  
  Purchase #2 $225.57   7.134%   $241.6622   $241.66   $241.65   $241.70  
  Purchase #3 $108.58   13.460%   $123.1949   $123.19   $123.20   $123.20  
  Purchase #4 $227.32   3.212%   $234.6215   $234.62   $234.60   $234.60  
  Purchase #5 $13.39   7.598%   $14.4074   $14.41   $14.40   $14.40  
  Purchase #6 $78.56   10.245%   $86.6085   $86.61   $86.60   $86.60  
  Purchase #7 $114.56   7.265%   $122.8828   $122.88   $122.90   $122.90  
  7 purchase totals = $952.95       $1,025.2036   $1,025.20   $1,025.20   $1,025.20