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 $92.78   10.173%   $102.2185   $102.22   $102.20   $102.20  
  Purchase #2 $159.73   11.265%   $177.7236   $177.72   $177.70   $177.70  
  Purchase #3 $240.58   12.494%   $270.6381   $270.64   $270.65   $270.60  
  Purchase #4 $21.62   8.131%   $23.3779   $23.38   $23.40   $23.40  
  Purchase #5 $86.55   7.374%   $92.9322   $92.93   $92.95   $92.90  
  Purchase #6 $24.46   13.407%   $27.7394   $27.74   $27.75   $27.70  
  Purchase #7 $171.66   9.532%   $188.0226   $188.02   $188.00   $188.00  
  7 purchase totals = $797.38       $882.6523   $882.65   $882.65   $882.50