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 $240.29   10.704%   $266.0106   $266.01   $266.00   $266.00  
  Purchase #2 $73.53   13.353%   $83.3485   $83.35   $83.35   $83.30  
  Purchase #3 $111.68   7.165%   $119.6819   $119.68   $119.70   $119.70  
  Purchase #4 $68.62   13.422%   $77.8302   $77.83   $77.85   $77.80  
  Purchase #5 $156.32   11.597%   $174.4484   $174.45   $174.45   $174.40  
  Purchase #6 $13.49   8.741%   $14.6692   $14.67   $14.65   $14.70  
  Purchase #7 $32.81   13.106%   $37.1101   $37.11   $37.10   $37.10  
  7 purchase totals = $696.74       $773.0989   $773.10   $773.10   $773.00