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 $123.76   8.779%   $134.6249   $134.62   $134.60   $134.60  
  Purchase #2 $172.88   10.634%   $191.2641   $191.26   $191.25   $191.30  
  Purchase #3 $123.77   8.260%   $133.9934   $133.99   $134.00   $134.00  
  Purchase #4 $188.29   5.127%   $197.9436   $197.94   $197.95   $197.90  
  Purchase #5 $197.54   4.105%   $205.649   $205.65   $205.65   $205.60  
  Purchase #6 $102.61   12.737%   $115.6794   $115.68   $115.70   $115.70  
  Purchase #7 $17.71   5.310%   $18.6504   $18.65   $18.65   $18.70  
  7 purchase totals = $926.56       $997.8048   $997.79   $997.80   $997.80