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 $57.69   6.712%   $61.5622   $61.56   $61.55   $61.60  
  Purchase #2 $246.80   3.715%   $255.9686   $255.97   $255.95   $256.00  
  Purchase #3 $152.84   8.503%   $165.836   $165.84   $165.85   $165.80  
  Purchase #4 $148.85   5.773%   $157.4431   $157.44   $157.45   $157.40  
  Purchase #5 $246.43   4.189%   $256.753   $256.75   $256.75   $256.80  
  Purchase #6 $228.78   12.867%   $258.2171   $258.22   $258.20   $258.20  
  Purchase #7 $225.83   7.544%   $242.8666   $242.87   $242.85   $242.90  
  7 purchase totals = $1,307.22       $1,398.6466   $1,398.65   $1,398.60   $1,398.70