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 $228.34   9.478%   $249.9821   $249.98   $250.00   $250.00  
  Purchase #2 $153.76   8.431%   $166.7235   $166.72   $166.70   $166.70  
  Purchase #3 $66.79   8.320%   $72.3469   $72.35   $72.35   $72.30  
  Purchase #4 $218.75   12.638%   $246.3956   $246.40   $246.40   $246.40  
  Purchase #5 $234.95   10.545%   $259.7255   $259.73   $259.75   $259.70  
  Purchase #6 $233.69   3.126%   $240.9951   $241.00   $241.00   $241.00  
  Purchase #7 $211.64   11.383%   $235.731   $235.73   $235.75   $235.70  
  7 purchase totals = $1,347.92       $1,471.8997   $1,471.91   $1,471.95   $1,471.80