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 $68.36   13.582%   $77.6447   $77.64   $77.65   $77.60  
  Purchase #2 $52.81   12.270%   $59.2898   $59.29   $59.30   $59.30  
  Purchase #3 $81.47   12.308%   $91.4973   $91.50   $91.50   $91.50  
  Purchase #4 $211.74   6.360%   $225.2067   $225.21   $225.20   $225.20  
  Purchase #5 $21.55   3.277%   $22.2562   $22.26   $22.25   $22.30  
  Purchase #6 $247.83   5.672%   $261.8869   $261.89   $261.90   $261.90  
  Purchase #7 $125.83   4.122%   $131.0167   $131.02   $131.00   $131.00  
  7 purchase totals = $809.59       $868.7983   $868.81   $868.80   $868.80