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 $55.92   12.664%   $63.0017   $63.00   $63.00   $63.00  
  Purchase #2 $61.45   13.357%   $69.6579   $69.66   $69.65   $69.70  
  Purchase #3 $221.38   3.219%   $228.5062   $228.51   $228.50   $228.50  
  Purchase #4 $10.42   9.466%   $11.4064   $11.41   $11.40   $11.40  
  Purchase #5 $231.61   3.369%   $239.4129   $239.41   $239.40   $239.40  
  Purchase #6 $97.92   3.548%   $101.3942   $101.39   $101.40   $101.40  
  Purchase #7 $77.96   12.429%   $87.6496   $87.65   $87.65   $87.60  
  7 purchase totals = $756.66       $801.0289   $801.03   $801.00   $801.00