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 $138.35   5.232%   $145.5885   $145.59   $145.60   $145.60  
  Purchase #2 $82.94   4.715%   $86.8506   $86.85   $86.85   $86.90  
  Purchase #3 $238.41   8.634%   $258.9943   $258.99   $259.00   $259.00  
  Purchase #4 $157.30   3.380%   $162.6167   $162.62   $162.60   $162.60  
  Purchase #5 $245.62   8.499%   $266.4952   $266.50   $266.50   $266.50  
  Purchase #6 $164.40   13.590%   $186.742   $186.74   $186.75   $186.70  
  Purchase #7 $144.82   5.429%   $152.6823   $152.68   $152.70   $152.70  
  7 purchase totals = $1,171.84       $1,259.9696   $1,259.97   $1,260.00   $1,260.00