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 $141.64   13.564%   $160.852   $160.85   $160.85   $160.90  
  Purchase #2 $205.94   10.439%   $227.4381   $227.44   $227.45   $227.40  
  Purchase #3 $42.27   13.203%   $47.8509   $47.85   $47.85   $47.90  
  Purchase #4 $226.46   4.588%   $236.85   $236.85   $236.85   $236.90  
  Purchase #5 $126.60   8.810%   $137.7535   $137.75   $137.75   $137.80  
  Purchase #6 $170.47   5.518%   $179.8765   $179.88   $179.90   $179.90  
  Purchase #7 $64.48   6.676%   $68.7847   $68.78   $68.80   $68.80  
  7 purchase totals = $977.86       $1,059.4057   $1,059.40   $1,059.45   $1,059.60