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 $222.86   5.195%   $234.4376   $234.44   $234.45   $234.40  
  Purchase #2 $216.76   13.874%   $246.8333   $246.83   $246.85   $246.80  
  Purchase #3 $13.56   5.141%   $14.2571   $14.26   $14.25   $14.30  
  Purchase #4 $104.88   3.116%   $108.1481   $108.15   $108.15   $108.10  
  Purchase #5 $215.99   6.278%   $229.5499   $229.55   $229.55   $229.50  
  Purchase #6 $68.71   6.184%   $72.959   $72.96   $72.95   $73.00  
  Purchase #7 $117.61   6.494%   $125.2476   $125.25   $125.25   $125.20  
  7 purchase totals = $960.37       $1,031.4326   $1,031.44   $1,031.45   $1,031.30