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 $188.73   9.516%   $206.6895   $206.69   $206.70   $206.70  
  Purchase #2 $64.54   4.520%   $67.4572   $67.46   $67.45   $67.50  
  Purchase #3 $28.57   8.355%   $30.957   $30.96   $30.95   $31.00  
  Purchase #4 $140.50   8.605%   $152.59   $152.59   $152.60   $152.60  
  Purchase #5 $19.53   8.592%   $21.208   $21.21   $21.20   $21.20  
  Purchase #6 $171.39   9.351%   $187.4167   $187.42   $187.40   $187.40  
  Purchase #7 $44.50   12.311%   $49.9784   $49.98   $50.00   $50.00  
  7 purchase totals = $657.76       $716.2968   $716.31   $716.30   $716.40