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 $110.59   7.724%   $119.132   $119.13   $119.15   $119.10  
  Purchase #2 $236.58   9.516%   $259.093   $259.09   $259.10   $259.10  
  Purchase #3 $84.55   8.451%   $91.6953   $91.70   $91.70   $91.70  
  Purchase #4 $59.94   4.503%   $62.6391   $62.64   $62.65   $62.60  
  Purchase #5 $186.97   7.473%   $200.9423   $200.94   $200.95   $200.90  
  Purchase #6 $43.91   7.640%   $47.2647   $47.26   $47.25   $47.30  
  Purchase #7 $201.43   6.490%   $214.5028   $214.50   $214.50   $214.50  
  7 purchase totals = $923.97       $995.2692   $995.26   $995.30   $995.20