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 $71.86   6.809%   $76.7529   $76.75   $76.75   $76.80  
  Purchase #2 $240.75   11.692%   $268.8985   $268.90   $268.90   $268.90  
  Purchase #3 $217.26   7.120%   $232.7289   $232.73   $232.75   $232.70  
  Purchase #4 $136.40   11.605%   $152.2292   $152.23   $152.25   $152.20  
  Purchase #5 $243.47   4.497%   $254.4188   $254.42   $254.40   $254.40  
  Purchase #6 $114.95   3.819%   $119.3399   $119.34   $119.35   $119.30  
  Purchase #7 $17.62   10.291%   $19.4333   $19.43   $19.45   $19.40  
  7 purchase totals = $1,042.31       $1,123.8015   $1,123.80   $1,123.85   $1,123.70