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 $23.92   11.166%   $26.5909   $26.59   $26.60   $26.60  
  Purchase #2 $249.76   6.254%   $265.38   $265.38   $265.40   $265.40  
  Purchase #3 $82.90   3.408%   $85.7252   $85.73   $85.75   $85.70  
  Purchase #4 $226.78   10.700%   $251.0455   $251.05   $251.05   $251.00  
  Purchase #5 $9.59   13.796%   $10.913   $10.91   $10.90   $10.90  
  Purchase #6 $52.39   8.507%   $56.8468   $56.85   $56.85   $56.80  
  Purchase #7 $196.78   7.242%   $211.0308   $211.03   $211.05   $211.00  
  7 purchase totals = $842.12       $907.5322   $907.54   $907.60   $907.40