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 $24.63   9.248%   $26.9078   $26.91   $26.90   $26.90  
  Purchase #2 $219.51   11.461%   $244.668   $244.67   $244.65   $244.70  
  Purchase #3 $61.48   3.759%   $63.791   $63.79   $63.80   $63.80  
  Purchase #4 $248.98   4.144%   $259.2977   $259.30   $259.30   $259.30  
  Purchase #5 $207.59   8.709%   $225.669   $225.67   $225.65   $225.70  
  Purchase #6 $72.31   5.369%   $76.1923   $76.19   $76.20   $76.20  
  Purchase #7 $205.49   4.742%   $215.2343   $215.23   $215.25   $215.20  
  7 purchase totals = $1,039.99       $1,111.7601   $1,111.76   $1,111.75   $1,111.80