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 $113.94   4.649%   $119.2371   $119.24   $119.25   $119.20  
  Purchase #2 $129.92   11.547%   $144.9219   $144.92   $144.90   $144.90  
  Purchase #3 $212.48   6.357%   $225.9874   $225.99   $226.00   $226.00  
  Purchase #4 $30.25   8.193%   $32.7284   $32.73   $32.75   $32.70  
  Purchase #5 $153.26   9.263%   $167.4565   $167.46   $167.45   $167.50  
  Purchase #6 $114.26   10.747%   $126.5395   $126.54   $126.55   $126.50  
  Purchase #7 $65.64   8.129%   $70.9759   $70.98   $71.00   $71.00  
  7 purchase totals = $819.75       $887.8467   $887.86   $887.90   $887.80