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 $206.76   13.789%   $235.2701   $235.27   $235.25   $235.30  
  Purchase #2 $201.75   11.866%   $225.6897   $225.69   $225.70   $225.70  
  Purchase #3 $61.90   6.569%   $65.9662   $65.97   $65.95   $66.00  
  Purchase #4 $123.91   7.302%   $132.9579   $132.96   $132.95   $133.00  
  Purchase #5 $113.77   3.259%   $117.4778   $117.48   $117.50   $117.50  
  Purchase #6 $8.96   8.816%   $9.7499   $9.75   $9.75   $9.70  
  Purchase #7 $126.79   12.693%   $142.8835   $142.88   $142.90   $142.90  
  7 purchase totals = $843.84       $929.9951   $930.00   $930.00   $930.10