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 $200.69   3.518%   $207.7503   $207.75   $207.75   $207.80  
  Purchase #2 $248.85   9.397%   $272.2344   $272.23   $272.25   $272.20  
  Purchase #3 $48.87   11.576%   $54.5272   $54.53   $54.55   $54.50  
  Purchase #4 $50.95   6.486%   $54.2546   $54.25   $54.25   $54.30  
  Purchase #5 $117.56   8.789%   $127.8923   $127.89   $127.90   $127.90  
  Purchase #6 $228.62   3.835%   $237.3876   $237.39   $237.40   $237.40  
  Purchase #7 $224.75   13.301%   $254.644   $254.64   $254.65   $254.60  
  7 purchase totals = $1,120.29       $1,208.6904   $1,208.68   $1,208.75   $1,208.70