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 $96.36   7.762%   $103.8395   $103.84   $103.85   $103.80  
  Purchase #2 $250.73   7.233%   $268.8653   $268.87   $268.85   $268.90  
  Purchase #3 $184.71   9.137%   $201.587   $201.59   $201.60   $201.60  
  Purchase #4 $27.84   5.591%   $29.3965   $29.40   $29.40   $29.40  
  Purchase #5 $127.99   9.541%   $140.2015   $140.20   $140.20   $140.20  
  Purchase #6 $21.75   12.297%   $24.4246   $24.42   $24.40   $24.40  
  Purchase #7 $17.38   7.111%   $18.6159   $18.62   $18.60   $18.60  
  7 purchase totals = $726.76       $786.9303   $786.94   $786.90   $786.90