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 $124.74   8.172%   $134.9338   $134.93   $134.95   $134.90  
  Purchase #2 $50.43   4.207%   $52.5516   $52.55   $52.55   $52.60  
  Purchase #3 $26.51   4.212%   $27.6266   $27.63   $27.65   $27.60  
  Purchase #4 $135.96   13.170%   $153.8659   $153.87   $153.85   $153.90  
  Purchase #5 $200.64   8.407%   $217.5078   $217.51   $217.50   $217.50  
  Purchase #6 $78.95   3.531%   $81.7377   $81.74   $81.75   $81.70  
  Purchase #7 $176.33   8.549%   $191.4045   $191.40   $191.40   $191.40  
  7 purchase totals = $793.56       $859.6279   $859.63   $859.65   $859.60