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 $88.30   11.483%   $98.4395   $98.44   $98.45   $98.40  
  Purchase #2 $27.76   3.564%   $28.7494   $28.75   $28.75   $28.70  
  Purchase #3 $104.34   4.609%   $109.149   $109.15   $109.15   $109.10  
  Purchase #4 $207.93   11.792%   $232.4491   $232.45   $232.45   $232.40  
  Purchase #5 $121.26   6.242%   $128.829   $128.83   $128.85   $128.80  
  Purchase #6 $97.35   4.207%   $101.4455   $101.45   $101.45   $101.40  
  Purchase #7 $76.85   12.766%   $86.6607   $86.66   $86.65   $86.70  
  7 purchase totals = $723.79       $785.7222   $785.73   $785.75   $785.50