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 $91.28   5.232%   $96.0558   $96.06   $96.05   $96.10  
  Purchase #2 $15.66   6.522%   $16.6813   $16.68   $16.70   $16.70  
  Purchase #3 $188.43   6.677%   $201.0115   $201.01   $201.00   $201.00  
  Purchase #4 $224.48   7.588%   $241.5135   $241.51   $241.50   $241.50  
  Purchase #5 $244.33   7.741%   $263.2436   $263.24   $263.25   $263.20  
  Purchase #6 $41.88   5.724%   $44.2772   $44.28   $44.30   $44.30  
  Purchase #7 $100.66   11.860%   $112.5983   $112.60   $112.60   $112.60  
  7 purchase totals = $906.72       $975.3812   $975.38   $975.40   $975.40