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 $119.83   5.291%   $126.1702   $126.17   $126.15   $126.20  
  Purchase #2 $134.39   8.813%   $146.2338   $146.23   $146.25   $146.20  
  Purchase #3 $13.35   5.149%   $14.0374   $14.04   $14.05   $14.00  
  Purchase #4 $33.73   3.609%   $34.9473   $34.95   $34.95   $34.90  
  Purchase #5 $204.71   7.770%   $220.616   $220.62   $220.60   $220.60  
  Purchase #6 $191.79   10.213%   $211.3775   $211.38   $211.40   $211.40  
  Purchase #7 $81.58   3.791%   $84.6727   $84.67   $84.65   $84.70  
  7 purchase totals = $779.38       $838.0549   $838.06   $838.05   $838.00