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 $48.54   12.448%   $54.5823   $54.58   $54.60   $54.60  
  Purchase #2 $118.56   8.870%   $129.0763   $129.08   $129.10   $129.10  
  Purchase #3 $171.66   13.832%   $195.404   $195.40   $195.40   $195.40  
  Purchase #4 $52.55   8.212%   $56.8654   $56.87   $56.85   $56.90  
  Purchase #5 $183.36   5.225%   $192.9406   $192.94   $192.95   $192.90  
  Purchase #6 $151.31   7.521%   $162.69   $162.69   $162.70   $162.70  
  Purchase #7 $227.93   11.662%   $254.5112   $254.51   $254.50   $254.50  
  7 purchase totals = $953.91       $1,046.0698   $1,046.07   $1,046.10   $1,046.10