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 $69.71   3.202%   $71.9421   $71.94   $71.95   $71.90  
  Purchase #2 $230.99   8.297%   $250.1552   $250.16   $250.15   $250.20  
  Purchase #3 $125.92   7.578%   $135.4622   $135.46   $135.45   $135.50  
  Purchase #4 $200.61   7.133%   $214.9195   $214.92   $214.90   $214.90  
  Purchase #5 $73.73   12.823%   $83.1844   $83.18   $83.20   $83.20  
  Purchase #6 $176.41   13.379%   $200.0119   $200.01   $200.00   $200.00  
  Purchase #7 $222.94   5.591%   $235.4046   $235.40   $235.40   $235.40  
  7 purchase totals = $1,100.31       $1,191.0799   $1,191.07   $1,191.05   $1,191.10