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 $81.59   11.808%   $91.2241   $91.22   $91.20   $91.20  
  Purchase #2 $182.90   13.562%   $207.7049   $207.70   $207.70   $207.70  
  Purchase #3 $83.56   11.655%   $93.2989   $93.30   $93.30   $93.30  
  Purchase #4 $46.83   3.786%   $48.603   $48.60   $48.60   $48.60  
  Purchase #5 $210.70   6.745%   $224.9117   $224.91   $224.90   $224.90  
  Purchase #6 $89.81   11.404%   $100.0519   $100.05   $100.05   $100.10  
  Purchase #7 $55.60   9.402%   $60.8275   $60.83   $60.85   $60.80  
  7 purchase totals = $750.99       $826.6220   $826.61   $826.60   $826.60