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 $28.26   13.736%   $32.1418   $32.14   $32.15   $32.10  
  Purchase #2 $197.76   10.403%   $218.333   $218.33   $218.35   $218.30  
  Purchase #3 $150.73   10.619%   $166.736   $166.74   $166.75   $166.70  
  Purchase #4 $135.93   4.183%   $141.616   $141.62   $141.60   $141.60  
  Purchase #5 $65.59   3.324%   $67.7702   $67.77   $67.75   $67.80  
  Purchase #6 $238.55   13.712%   $271.26   $271.26   $271.25   $271.30  
  Purchase #7 $168.28   8.254%   $182.1698   $182.17   $182.15   $182.20  
  7 purchase totals = $985.10       $1,080.0268   $1,080.03   $1,080.00   $1,080.00