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 $234.69   7.779%   $252.9465   $252.95   $252.95   $252.90  
  Purchase #2 $171.97   9.788%   $188.8024   $188.80   $188.80   $188.80  
  Purchase #3 $14.56   7.604%   $15.6671   $15.67   $15.65   $15.70  
  Purchase #4 $125.62   4.323%   $131.0506   $131.05   $131.05   $131.10  
  Purchase #5 $186.66   9.671%   $204.7119   $204.71   $204.70   $204.70  
  Purchase #6 $132.84   11.591%   $148.2375   $148.24   $148.25   $148.20  
  Purchase #7 $57.75   13.395%   $65.4856   $65.49   $65.50   $65.50  
  7 purchase totals = $924.09       $1,006.9016   $1,006.91   $1,006.90   $1,006.90