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 $67.79   3.189%   $69.9518   $69.95   $69.95   $70.00  
  Purchase #2 $189.27   8.856%   $206.0318   $206.03   $206.05   $206.00  
  Purchase #3 $81.53   11.283%   $90.729   $90.73   $90.75   $90.70  
  Purchase #4 $181.46   7.249%   $194.614   $194.61   $194.60   $194.60  
  Purchase #5 $188.48   11.272%   $209.7255   $209.73   $209.75   $209.70  
  Purchase #6 $211.71   6.577%   $225.6342   $225.63   $225.65   $225.60  
  Purchase #7 $30.32   5.852%   $32.0943   $32.09   $32.10   $32.10  
  7 purchase totals = $950.56       $1,028.7806   $1,028.77   $1,028.85   $1,028.70