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 $167.44   10.261%   $184.621   $184.62   $184.60   $184.60  
  Purchase #2 $39.80   5.156%   $41.8521   $41.85   $41.85   $41.90  
  Purchase #3 $8.91   4.257%   $9.2893   $9.29   $9.30   $9.30  
  Purchase #4 $178.58   5.161%   $187.7965   $187.80   $187.80   $187.80  
  Purchase #5 $59.80   13.544%   $67.8993   $67.90   $67.90   $67.90  
  Purchase #6 $109.45   3.452%   $113.2282   $113.23   $113.25   $113.20  
  Purchase #7 $172.92   10.383%   $190.8743   $190.87   $190.85   $190.90  
  7 purchase totals = $736.90       $795.5607   $795.56   $795.55   $795.60