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 $239.93   8.203%   $259.6115   $259.61   $259.60   $259.60  
  Purchase #2 $225.31   13.483%   $255.6885   $255.69   $255.70   $255.70  
  Purchase #3 $17.61   5.360%   $18.5539   $18.55   $18.55   $18.60  
  Purchase #4 $198.36   10.555%   $219.2969   $219.30   $219.30   $219.30  
  Purchase #5 $61.54   3.648%   $63.785   $63.79   $63.80   $63.80  
  Purchase #6 $212.29   11.253%   $236.179   $236.18   $236.20   $236.20  
  Purchase #7 $100.66   13.110%   $113.8565   $113.86   $113.85   $113.90  
  7 purchase totals = $1,055.70       $1,166.9713   $1,166.98   $1,167.00   $1,167.10