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 $144.49   11.519%   $161.1338   $161.13   $161.15   $161.10  
  Purchase #2 $248.35   6.665%   $264.9025   $264.90   $264.90   $264.90  
  Purchase #3 $114.61   4.382%   $119.6322   $119.63   $119.65   $119.60  
  Purchase #4 $196.76   8.612%   $213.705   $213.71   $213.70   $213.70  
  Purchase #5 $219.83   12.187%   $246.6207   $246.62   $246.60   $246.60  
  Purchase #6 $67.44   4.225%   $70.2893   $70.29   $70.30   $70.30  
  Purchase #7 $68.35   12.619%   $76.9751   $76.98   $77.00   $77.00  
  7 purchase totals = $1,059.83       $1,153.2586   $1,153.26   $1,153.30   $1,153.20