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 $187.86   10.202%   $207.0255   $207.03   $207.05   $207.00  
  Purchase #2 $179.30   10.216%   $197.6173   $197.62   $197.60   $197.60  
  Purchase #3 $80.41   6.571%   $85.6937   $85.69   $85.70   $85.70  
  Purchase #4 $66.29   13.396%   $75.1702   $75.17   $75.15   $75.20  
  Purchase #5 $70.63   8.445%   $76.5947   $76.59   $76.60   $76.60  
  Purchase #6 $129.74   8.751%   $141.0935   $141.09   $141.10   $141.10  
  Purchase #7 $101.95   10.654%   $112.8118   $112.81   $112.80   $112.80  
  7 purchase totals = $816.18       $896.0067   $896.00   $896.00   $896.00