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 $156.54   10.798%   $173.4432   $173.44   $173.45   $173.40  
  Purchase #2 $219.38   3.338%   $226.7029   $226.70   $226.70   $226.70  
  Purchase #3 $209.32   3.616%   $216.889   $216.89   $216.90   $216.90  
  Purchase #4 $204.66   8.358%   $221.7655   $221.77   $221.75   $221.80  
  Purchase #5 $57.26   11.133%   $63.6348   $63.63   $63.65   $63.60  
  Purchase #6 $82.28   3.637%   $85.2725   $85.27   $85.25   $85.30  
  Purchase #7 $186.71   12.649%   $210.3269   $210.33   $210.35   $210.30  
  7 purchase totals = $1,116.15       $1,198.0348   $1,198.03   $1,198.05   $1,198.00