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 $82.57   12.493%   $92.8855   $92.89   $92.90   $92.90  
  Purchase #2 $185.85   10.447%   $205.2657   $205.27   $205.25   $205.30  
  Purchase #3 $46.26   7.641%   $49.7947   $49.79   $49.80   $49.80  
  Purchase #4 $168.89   8.802%   $183.7557   $183.76   $183.75   $183.80  
  Purchase #5 $12.90   10.608%   $14.2684   $14.27   $14.25   $14.30  
  Purchase #6 $43.52   7.539%   $46.801   $46.80   $46.80   $46.80  
  Purchase #7 $220.51   13.189%   $249.5931   $249.59   $249.60   $249.60  
  7 purchase totals = $760.50       $842.3641   $842.37   $842.35   $842.50