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 $103.27   12.279%   $115.9505   $115.95   $115.95   $116.00  
  Purchase #2 $157.89   13.825%   $179.7183   $179.72   $179.70   $179.70  
  Purchase #3 $241.75   4.202%   $251.9083   $251.91   $251.90   $251.90  
  Purchase #4 $209.58   6.514%   $223.232   $223.23   $223.25   $223.20  
  Purchase #5 $89.67   9.693%   $98.3617   $98.36   $98.35   $98.40  
  Purchase #6 $103.61   13.605%   $117.7061   $117.71   $117.70   $117.70  
  Purchase #7 $223.81   11.337%   $249.1833   $249.18   $249.20   $249.20  
  7 purchase totals = $1,129.58       $1,236.0602   $1,236.06   $1,236.05   $1,236.10