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 $246.62   9.294%   $269.5409   $269.54   $269.55   $269.50  
  Purchase #2 $69.34   6.269%   $73.6869   $73.69   $73.70   $73.70  
  Purchase #3 $148.85   5.819%   $157.5116   $157.51   $157.50   $157.50  
  Purchase #4 $77.41   12.214%   $86.8649   $86.86   $86.85   $86.90  
  Purchase #5 $198.29   11.601%   $221.2936   $221.29   $221.30   $221.30  
  Purchase #6 $43.51   12.757%   $49.0606   $49.06   $49.05   $49.10  
  Purchase #7 $62.49   3.856%   $64.8996   $64.90   $64.90   $64.90  
  7 purchase totals = $846.51       $922.8581   $922.85   $922.85   $922.90