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 $119.71   12.552%   $134.736   $134.74   $134.75   $134.70  
  Purchase #2 $245.81   5.394%   $259.069   $259.07   $259.05   $259.10  
  Purchase #3 $125.28   8.250%   $135.6156   $135.62   $135.60   $135.60  
  Purchase #4 $40.80   6.788%   $43.5695   $43.57   $43.55   $43.60  
  Purchase #5 $77.39   3.413%   $80.0313   $80.03   $80.05   $80.00  
  Purchase #6 $176.71   13.160%   $199.965   $199.97   $199.95   $200.00  
  Purchase #7 $24.97   10.797%   $27.666   $27.67   $27.65   $27.70  
  7 purchase totals = $810.67       $880.6524   $880.67   $880.60   $880.70