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 $222.97   10.343%   $246.0318   $246.03   $246.05   $246.00  
  Purchase #2 $126.56   8.173%   $136.9037   $136.90   $136.90   $136.90  
  Purchase #3 $118.65   4.620%   $124.1316   $124.13   $124.15   $124.10  
  Purchase #4 $73.55   3.670%   $76.2493   $76.25   $76.25   $76.20  
  Purchase #5 $62.29   12.217%   $69.9   $69.90   $69.90   $69.90  
  Purchase #6 $57.85   6.666%   $61.7063   $61.71   $61.70   $61.70  
  Purchase #7 $218.69   7.336%   $234.7331   $234.73   $234.75   $234.70  
  7 purchase totals = $880.56       $949.6558   $949.65   $949.70   $949.50