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 $83.26   3.517%   $86.1883   $86.19   $86.20   $86.20  
  Purchase #2 $224.98   9.844%   $247.127   $247.13   $247.15   $247.10  
  Purchase #3 $63.94   12.217%   $71.7515   $71.75   $71.75   $71.80  
  Purchase #4 $196.35   7.318%   $210.7189   $210.72   $210.70   $210.70  
  Purchase #5 $60.86   8.629%   $66.1116   $66.11   $66.10   $66.10  
  Purchase #6 $30.35   9.275%   $33.165   $33.17   $33.15   $33.20  
  Purchase #7 $223.67   11.181%   $248.6785   $248.68   $248.70   $248.70  
  7 purchase totals = $883.41       $963.7408   $963.75   $963.75   $963.80