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 $92.77   6.204%   $98.5255   $98.53   $98.55   $98.50  
  Purchase #2 $210.54   11.628%   $235.0216   $235.02   $235.00   $235.00  
  Purchase #3 $81.66   10.300%   $90.071   $90.07   $90.05   $90.10  
  Purchase #4 $165.99   13.585%   $188.5397   $188.54   $188.55   $188.50  
  Purchase #5 $177.63   4.798%   $186.1527   $186.15   $186.15   $186.20  
  Purchase #6 $60.54   7.176%   $64.8844   $64.88   $64.90   $64.90  
  Purchase #7 $180.74   4.495%   $188.8643   $188.86   $188.85   $188.90  
  7 purchase totals = $969.87       $1,052.0592   $1,052.05   $1,052.05   $1,052.10