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 $53.36   8.543%   $57.9185   $57.92   $57.90   $57.90  
  Purchase #2 $76.81   12.655%   $86.5303   $86.53   $86.55   $86.50  
  Purchase #3 $176.28   7.779%   $189.9928   $189.99   $190.00   $190.00  
  Purchase #4 $24.57   7.462%   $26.4034   $26.40   $26.40   $26.40  
  Purchase #5 $204.61   9.193%   $223.4198   $223.42   $223.40   $223.40  
  Purchase #6 $92.56   12.360%   $104.0004   $104.00   $104.00   $104.00  
  Purchase #7 $40.62   8.396%   $44.0305   $44.03   $44.05   $44.00  
  7 purchase totals = $668.81       $732.2957   $732.29   $732.30   $732.20