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 $248.65   13.316%   $281.7602   $281.76   $281.75   $281.80  
  Purchase #2 $34.93   12.219%   $39.1981   $39.20   $39.20   $39.20  
  Purchase #3 $73.69   6.382%   $78.3929   $78.39   $78.40   $78.40  
  Purchase #4 $180.54   9.733%   $198.112   $198.11   $198.10   $198.10  
  Purchase #5 $40.96   13.445%   $46.4671   $46.47   $46.45   $46.50  
  Purchase #6 $199.79   8.459%   $216.6902   $216.69   $216.70   $216.70  
  Purchase #7 $201.41   12.183%   $225.9478   $225.95   $225.95   $225.90  
  7 purchase totals = $979.97       $1,086.5683   $1,086.57   $1,086.55   $1,086.60