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 $246.48   7.511%   $264.9931   $264.99   $265.00   $265.00  
  Purchase #2 $41.49   6.819%   $44.3192   $44.32   $44.30   $44.30  
  Purchase #3 $12.87   7.775%   $13.8706   $13.87   $13.85   $13.90  
  Purchase #4 $56.81   10.575%   $62.8177   $62.82   $62.80   $62.80  
  Purchase #5 $56.34   5.121%   $59.2252   $59.23   $59.25   $59.20  
  Purchase #6 $177.38   3.873%   $184.2499   $184.25   $184.25   $184.20  
  Purchase #7 $165.30   11.532%   $184.3624   $184.36   $184.35   $184.40  
  7 purchase totals = $756.67       $813.8381   $813.84   $813.80   $813.80