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 $24.27   8.773%   $26.3992   $26.40   $26.40   $26.40  
  Purchase #2 $110.90   6.639%   $118.2627   $118.26   $118.25   $118.30  
  Purchase #3 $186.68   4.722%   $195.495   $195.50   $195.50   $195.50  
  Purchase #4 $189.77   8.464%   $205.8321   $205.83   $205.85   $205.80  
  Purchase #5 $56.57   11.384%   $63.0099   $63.01   $63.00   $63.00  
  Purchase #6 $86.94   7.766%   $93.6918   $93.69   $93.70   $93.70  
  Purchase #7 $37.94   10.471%   $41.9127   $41.91   $41.90   $41.90  
  7 purchase totals = $693.07       $744.6034   $744.60   $744.60   $744.60