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 $59.31   11.123%   $65.9071   $65.91   $65.90   $65.90  
  Purchase #2 $168.78   10.337%   $186.2268   $186.23   $186.25   $186.20  
  Purchase #3 $97.85   13.622%   $111.1791   $111.18   $111.20   $111.20  
  Purchase #4 $154.74   13.112%   $175.0295   $175.03   $175.05   $175.00  
  Purchase #5 $74.25   8.693%   $80.7046   $80.70   $80.70   $80.70  
  Purchase #6 $66.73   3.125%   $68.8153   $68.82   $68.80   $68.80  
  Purchase #7 $118.41   4.197%   $123.3797   $123.38   $123.40   $123.40  
  7 purchase totals = $740.07       $811.2421   $811.25   $811.30   $811.20