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 $14.95   13.548%   $16.9754   $16.98   $17.00   $17.00  
  Purchase #2 $136.95   9.121%   $149.4412   $149.44   $149.45   $149.40  
  Purchase #3 $117.92   5.501%   $124.4068   $124.41   $124.40   $124.40  
  Purchase #4 $113.78   9.358%   $124.4275   $124.43   $124.45   $124.40  
  Purchase #5 $177.95   11.657%   $198.6936   $198.69   $198.70   $198.70  
  Purchase #6 $127.72   11.779%   $142.7641   $142.76   $142.75   $142.80  
  Purchase #7 $87.98   8.556%   $95.5076   $95.51   $95.50   $95.50  
  7 purchase totals = $777.25       $852.2162   $852.22   $852.25   $852.20