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 $206.68   13.782%   $235.1646   $235.16   $235.15   $235.20  
  Purchase #2 $193.27   9.544%   $211.7157   $211.72   $211.70   $211.70  
  Purchase #3 $15.79   13.426%   $17.91   $17.91   $17.90   $17.90  
  Purchase #4 $53.34   13.189%   $60.375   $60.38   $60.40   $60.40  
  Purchase #5 $202.99   10.229%   $223.7538   $223.75   $223.75   $223.80  
  Purchase #6 $229.42   3.781%   $238.0944   $238.09   $238.10   $238.10  
  Purchase #7 $117.81   7.505%   $126.6516   $126.65   $126.65   $126.70  
  7 purchase totals = $1,019.30       $1,113.6651   $1,113.66   $1,113.65   $1,113.80