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 $117.61   6.454%   $125.2005   $125.20   $125.20   $125.20  
  Purchase #2 $46.54   10.396%   $51.3783   $51.38   $51.40   $51.40  
  Purchase #3 $15.50   13.639%   $17.614   $17.61   $17.60   $17.60  
  Purchase #4 $231.60   9.686%   $254.0328   $254.03   $254.05   $254.00  
  Purchase #5 $83.99   11.181%   $93.3809   $93.38   $93.40   $93.40  
  Purchase #6 $30.93   4.429%   $32.2999   $32.30   $32.30   $32.30  
  Purchase #7 $181.72   11.239%   $202.1435   $202.14   $202.15   $202.10  
  7 purchase totals = $707.89       $776.0499   $776.04   $776.10   $776.00