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 $238.50   5.465%   $251.534   $251.53   $251.55   $251.50  
  Purchase #2 $122.88   9.527%   $134.5868   $134.59   $134.60   $134.60  
  Purchase #3 $68.27   4.569%   $71.3893   $71.39   $71.40   $71.40  
  Purchase #4 $130.91   7.147%   $140.2661   $140.27   $140.25   $140.30  
  Purchase #5 $161.33   3.212%   $166.5119   $166.51   $166.50   $166.50  
  Purchase #6 $104.84   9.841%   $115.1573   $115.16   $115.15   $115.20  
  Purchase #7 $72.46   4.189%   $75.4953   $75.50   $75.50   $75.50  
  7 purchase totals = $899.19       $954.9407   $954.95   $954.95   $955.00