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 $248.49   13.401%   $281.7901   $281.79   $281.80   $281.80  
  Purchase #2 $26.98   3.811%   $28.0082   $28.01   $28.00   $28.00  
  Purchase #3 $12.68   10.426%   $14.002   $14.00   $14.00   $14.00  
  Purchase #4 $24.67   6.591%   $26.296   $26.30   $26.30   $26.30  
  Purchase #5 $101.49   3.426%   $104.967   $104.97   $104.95   $105.00  
  Purchase #6 $52.66   13.345%   $59.6875   $59.69   $59.70   $59.70  
  Purchase #7 $131.95   5.424%   $139.107   $139.11   $139.10   $139.10  
  7 purchase totals = $598.92       $653.8578   $653.87   $653.85   $653.90