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 $235.54   13.674%   $267.7477   $267.75   $267.75   $267.70  
  Purchase #2 $23.97   9.655%   $26.2843   $26.28   $26.30   $26.30  
  Purchase #3 $238.81   9.517%   $261.5375   $261.54   $261.55   $261.50  
  Purchase #4 $203.91   4.524%   $213.1349   $213.13   $213.15   $213.10  
  Purchase #5 $58.43   12.415%   $65.6841   $65.68   $65.70   $65.70  
  Purchase #6 $27.66   11.580%   $30.863   $30.86   $30.85   $30.90  
  Purchase #7 $18.40   12.626%   $20.7232   $20.72   $20.70   $20.70  
  7 purchase totals = $806.72       $885.9747   $885.96   $886.00   $885.90