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 $208.61   8.642%   $226.6381   $226.64   $226.65   $226.60  
  Purchase #2 $24.57   5.761%   $25.9855   $25.99   $26.00   $26.00  
  Purchase #3 $208.39   11.280%   $231.8964   $231.90   $231.90   $231.90  
  Purchase #4 $61.99   12.446%   $69.7053   $69.71   $69.70   $69.70  
  Purchase #5 $238.66   12.710%   $268.9937   $268.99   $269.00   $269.00  
  Purchase #6 $88.42   3.703%   $91.6942   $91.69   $91.70   $91.70  
  Purchase #7 $82.26   4.233%   $85.7421   $85.74   $85.75   $85.70  
  7 purchase totals = $912.90       $1,000.6553   $1,000.66   $1,000.70   $1,000.60