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 $117.58   7.708%   $126.6431   $126.64   $126.65   $126.60  
  Purchase #2 $138.71   4.272%   $144.6357   $144.64   $144.65   $144.60  
  Purchase #3 $118.30   9.872%   $129.9786   $129.98   $130.00   $130.00  
  Purchase #4 $231.82   13.724%   $263.635   $263.64   $263.65   $263.60  
  Purchase #5 $232.84   11.681%   $260.038   $260.04   $260.05   $260.00  
  Purchase #6 $51.65   8.835%   $56.2133   $56.21   $56.20   $56.20  
  Purchase #7 $198.75   9.208%   $217.0509   $217.05   $217.05   $217.10  
  7 purchase totals = $1,089.65       $1,198.1946   $1,198.20   $1,198.25   $1,198.10