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 $232.77   13.748%   $264.7712   $264.77   $264.75   $264.80  
  Purchase #2 $227.48   13.149%   $257.3913   $257.39   $257.40   $257.40  
  Purchase #3 $206.41   4.236%   $215.1535   $215.15   $215.15   $215.20  
  Purchase #4 $37.76   12.396%   $42.4407   $42.44   $42.45   $42.40  
  Purchase #5 $114.73   7.852%   $123.7386   $123.74   $123.75   $123.70  
  Purchase #6 $41.77   5.701%   $44.1513   $44.15   $44.15   $44.20  
  Purchase #7 $18.26   12.683%   $20.5759   $20.58   $20.60   $20.60  
  7 purchase totals = $879.18       $968.2225   $968.22   $968.25   $968.30