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 $157.78   8.188%   $170.699   $170.70   $170.70   $170.70  
  Purchase #2 $151.86   12.354%   $170.6208   $170.62   $170.60   $170.60  
  Purchase #3 $81.84   3.727%   $84.8902   $84.89   $84.90   $84.90  
  Purchase #4 $46.98   3.630%   $48.6854   $48.69   $48.70   $48.70  
  Purchase #5 $233.91   9.705%   $256.611   $256.61   $256.60   $256.60  
  Purchase #6 $131.50   5.288%   $138.4537   $138.45   $138.45   $138.50  
  Purchase #7 $178.27   3.380%   $184.2955   $184.30   $184.30   $184.30  
  7 purchase totals = $982.14       $1,054.2556   $1,054.26   $1,054.25   $1,054.30