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 $71.62   6.460%   $76.2467   $76.25   $76.25   $76.20  
  Purchase #2 $162.49   6.388%   $172.8699   $172.87   $172.85   $172.90  
  Purchase #3 $246.79   8.651%   $268.1398   $268.14   $268.15   $268.10  
  Purchase #4 $198.89   4.300%   $207.4423   $207.44   $207.45   $207.40  
  Purchase #5 $170.83   13.832%   $194.4592   $194.46   $194.45   $194.50  
  Purchase #6 $240.67   8.188%   $260.3761   $260.38   $260.40   $260.40  
  Purchase #7 $27.79   9.558%   $30.4462   $30.45   $30.45   $30.40  
  7 purchase totals = $1,119.08       $1,209.9802   $1,209.99   $1,210.00   $1,209.90