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 $118.47   6.354%   $125.9976   $126.00   $126.00   $126.00  
  Purchase #2 $209.95   8.698%   $228.2115   $228.21   $228.20   $228.20  
  Purchase #3 $174.97   7.840%   $188.6876   $188.69   $188.70   $188.70  
  Purchase #4 $175.93   10.543%   $194.4783   $194.48   $194.50   $194.50  
  Purchase #5 $16.61   3.577%   $17.2041   $17.20   $17.20   $17.20  
  Purchase #6 $194.69   13.825%   $221.6059   $221.61   $221.60   $221.60  
  Purchase #7 $29.73   3.134%   $30.6617   $30.66   $30.65   $30.70  
  7 purchase totals = $920.35       $1,006.8467   $1,006.85   $1,006.85   $1,006.90