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 $59.31   11.628%   $66.2066   $66.21   $66.20   $66.20  
  Purchase #2 $151.63   8.720%   $164.8521   $164.85   $164.85   $164.90  
  Purchase #3 $114.86   6.340%   $122.1421   $122.14   $122.15   $122.10  
  Purchase #4 $162.29   11.534%   $181.0085   $181.01   $181.00   $181.00  
  Purchase #5 $70.59   3.690%   $73.1948   $73.19   $73.20   $73.20  
  Purchase #6 $237.42   13.673%   $269.8824   $269.88   $269.90   $269.90  
  Purchase #7 $51.38   5.147%   $54.0245   $54.02   $54.00   $54.00  
  7 purchase totals = $847.48       $931.3110   $931.30   $931.30   $931.30