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 $76.66   10.804%   $84.9423   $84.94   $84.95   $84.90  
  Purchase #2 $221.79   8.432%   $240.4913   $240.49   $240.50   $240.50  
  Purchase #3 $174.31   11.357%   $194.1064   $194.11   $194.10   $194.10  
  Purchase #4 $162.45   8.801%   $176.7472   $176.75   $176.75   $176.70  
  Purchase #5 $162.26   5.188%   $170.678   $170.68   $170.70   $170.70  
  Purchase #6 $243.37   5.521%   $256.8065   $256.81   $256.80   $256.80  
  Purchase #7 $206.36   10.425%   $227.873   $227.87   $227.85   $227.90  
  7 purchase totals = $1,247.20       $1,351.6447   $1,351.65   $1,351.65   $1,351.60