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 $182.61   6.208%   $193.9464   $193.95   $193.95   $193.90  
  Purchase #2 $87.57   3.817%   $90.9125   $90.91   $90.90   $90.90  
  Purchase #3 $229.51   6.834%   $245.1947   $245.19   $245.20   $245.20  
  Purchase #4 $202.44   4.846%   $212.2502   $212.25   $212.25   $212.30  
  Purchase #5 $214.32   6.637%   $228.5444   $228.54   $228.55   $228.50  
  Purchase #6 $208.70   3.143%   $215.2594   $215.26   $215.25   $215.30  
  Purchase #7 $148.66   10.559%   $164.357   $164.36   $164.35   $164.40  
  7 purchase totals = $1,273.81       $1,350.4646   $1,350.46   $1,350.45   $1,350.50