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 $200.78   12.383%   $225.6426   $225.64   $225.65   $225.60  
  Purchase #2 $227.89   13.404%   $258.4364   $258.44   $258.45   $258.40  
  Purchase #3 $44.74   4.542%   $46.7721   $46.77   $46.75   $46.80  
  Purchase #4 $208.80   3.330%   $215.753   $215.75   $215.75   $215.80  
  Purchase #5 $112.83   12.156%   $126.5456   $126.55   $126.55   $126.50  
  Purchase #6 $175.47   4.729%   $183.768   $183.77   $183.75   $183.80  
  Purchase #7 $13.67   12.786%   $15.4178   $15.42   $15.40   $15.40  
  7 purchase totals = $984.18       $1,072.3355   $1,072.34   $1,072.30   $1,072.30