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 $246.96   8.518%   $267.9961   $268.00   $268.00   $268.00  
  Purchase #2 $111.61   7.114%   $119.5499   $119.55   $119.55   $119.50  
  Purchase #3 $30.83   10.841%   $34.1723   $34.17   $34.15   $34.20  
  Purchase #4 $184.42   12.285%   $207.076   $207.08   $207.10   $207.10  
  Purchase #5 $26.69   10.307%   $29.4409   $29.44   $29.45   $29.40  
  Purchase #6 $83.54   12.743%   $94.1855   $94.19   $94.20   $94.20  
  Purchase #7 $108.87   4.577%   $113.853   $113.85   $113.85   $113.90  
  7 purchase totals = $792.92       $866.2737   $866.28   $866.30   $866.30