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 $23.34   11.152%   $25.9429   $25.94   $25.95   $25.90  
  Purchase #2 $90.96   3.298%   $93.9599   $93.96   $93.95   $94.00  
  Purchase #3 $202.55   12.675%   $228.2232   $228.22   $228.20   $228.20  
  Purchase #4 $69.83   4.280%   $72.8187   $72.82   $72.80   $72.80  
  Purchase #5 $247.81   7.396%   $266.138   $266.14   $266.15   $266.10  
  Purchase #6 $45.80   10.863%   $50.7753   $50.78   $50.80   $50.80  
  Purchase #7 $152.68   6.217%   $162.1721   $162.17   $162.15   $162.20  
  7 purchase totals = $832.97       $900.0301   $900.03   $900.00   $900.00