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 $119.46   6.133%   $126.7865   $126.79   $126.80   $126.80  
  Purchase #2 $42.47   3.738%   $44.0575   $44.06   $44.05   $44.10  
  Purchase #3 $164.71   13.711%   $187.2934   $187.29   $187.30   $187.30  
  Purchase #4 $8.94   11.650%   $9.9815   $9.98   $10.00   $10.00  
  Purchase #5 $180.71   4.358%   $188.5853   $188.59   $188.60   $188.60  
  Purchase #6 $201.64   7.868%   $217.505   $217.51   $217.50   $217.50  
  Purchase #7 $246.86   7.449%   $265.2486   $265.25   $265.25   $265.20  
  7 purchase totals = $964.79       $1,039.4578   $1,039.47   $1,039.50   $1,039.50