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 $54.66   13.257%   $61.9063   $61.91   $61.90   $61.90  
  Purchase #2 $74.32   10.843%   $82.3785   $82.38   $82.40   $82.40  
  Purchase #3 $168.71   10.706%   $186.7721   $186.77   $186.75   $186.80  
  Purchase #4 $68.60   9.268%   $74.9578   $74.96   $74.95   $75.00  
  Purchase #5 $145.48   12.254%   $163.3071   $163.31   $163.30   $163.30  
  Purchase #6 $217.78   10.162%   $239.9108   $239.91   $239.90   $239.90  
  Purchase #7 $41.75   13.138%   $47.2351   $47.24   $47.25   $47.20  
  7 purchase totals = $771.30       $856.4677   $856.48   $856.45   $856.50