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 $189.41   8.586%   $205.6727   $205.67   $205.65   $205.70  
  Purchase #2 $22.92   12.214%   $25.7194   $25.72   $25.70   $25.70  
  Purchase #3 $133.69   8.385%   $144.8999   $144.90   $144.90   $144.90  
  Purchase #4 $111.43   9.271%   $121.7607   $121.76   $121.75   $121.80  
  Purchase #5 $46.88   6.440%   $49.8991   $49.90   $49.90   $49.90  
  Purchase #6 $244.99   4.683%   $256.4629   $256.46   $256.45   $256.50  
  Purchase #7 $126.50   4.287%   $131.9231   $131.92   $131.90   $131.90  
  7 purchase totals = $875.82       $936.3378   $936.33   $936.25   $936.40