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 $240.77   5.426%   $253.8342   $253.83   $253.85   $253.80  
  Purchase #2 $160.26   10.197%   $176.6017   $176.60   $176.60   $176.60  
  Purchase #3 $119.55   8.382%   $129.5707   $129.57   $129.55   $129.60  
  Purchase #4 $165.74   5.368%   $174.6369   $174.64   $174.65   $174.60  
  Purchase #5 $43.91   9.565%   $48.11   $48.11   $48.10   $48.10  
  Purchase #6 $226.48   13.784%   $257.698   $257.70   $257.70   $257.70  
  Purchase #7 $88.60   9.683%   $97.1791   $97.18   $97.20   $97.20  
  7 purchase totals = $1,045.31       $1,137.6306   $1,137.63   $1,137.65   $1,137.60