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 $162.68   12.706%   $183.3501   $183.35   $183.35   $183.40  
  Purchase #2 $120.26   3.194%   $124.1011   $124.10   $124.10   $124.10  
  Purchase #3 $122.98   13.312%   $139.3511   $139.35   $139.35   $139.40  
  Purchase #4 $32.68   9.446%   $35.767   $35.77   $35.75   $35.80  
  Purchase #5 $177.66   10.599%   $196.4902   $196.49   $196.50   $196.50  
  Purchase #6 $113.73   4.377%   $118.708   $118.71   $118.70   $118.70  
  Purchase #7 $247.94   6.465%   $263.9693   $263.97   $263.95   $264.00  
  7 purchase totals = $977.93       $1,061.7368   $1,061.74   $1,061.70   $1,061.90