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 $54.71   13.158%   $61.9087   $61.91   $61.90   $61.90  
  Purchase #2 $193.61   8.604%   $210.2682   $210.27   $210.25   $210.30  
  Purchase #3 $235.43   9.350%   $257.4427   $257.44   $257.45   $257.40  
  Purchase #4 $29.51   11.745%   $32.9759   $32.98   $33.00   $33.00  
  Purchase #5 $198.46   8.527%   $215.3827   $215.38   $215.40   $215.40  
  Purchase #6 $87.65   12.724%   $98.8026   $98.80   $98.80   $98.80  
  Purchase #7 $138.27   10.406%   $152.6584   $152.66   $152.65   $152.70  
  7 purchase totals = $937.64       $1,029.4392   $1,029.44   $1,029.45   $1,029.50