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 $114.27   9.416%   $125.0297   $125.03   $125.05   $125.00  
  Purchase #2 $152.38   11.735%   $170.2618   $170.26   $170.25   $170.30  
  Purchase #3 $84.85   10.604%   $93.8475   $93.85   $93.85   $93.80  
  Purchase #4 $190.29   8.658%   $206.7653   $206.77   $206.75   $206.80  
  Purchase #5 $29.61   3.748%   $30.7198   $30.72   $30.70   $30.70  
  Purchase #6 $249.73   7.696%   $268.9492   $268.95   $268.95   $268.90  
  Purchase #7 $176.69   5.265%   $185.9927   $185.99   $186.00   $186.00  
  7 purchase totals = $997.82       $1,081.5660   $1,081.57   $1,081.55   $1,081.50