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 $186.29   11.631%   $207.9574   $207.96   $207.95   $208.00  
  Purchase #2 $50.48   5.205%   $53.1075   $53.11   $53.10   $53.10  
  Purchase #3 $237.34   12.496%   $266.998   $267.00   $267.00   $267.00  
  Purchase #4 $121.36   4.207%   $126.4656   $126.47   $126.45   $126.50  
  Purchase #5 $241.86   8.579%   $262.6092   $262.61   $262.60   $262.60  
  Purchase #6 $112.78   12.507%   $126.8854   $126.89   $126.90   $126.90  
  Purchase #7 $40.88   6.536%   $43.5519   $43.55   $43.55   $43.60  
  7 purchase totals = $990.99       $1,087.5750   $1,087.59   $1,087.55   $1,087.70