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 $161.37   13.243%   $182.7402   $182.74   $182.75   $182.70  
  Purchase #2 $32.61   8.388%   $35.3453   $35.35   $35.35   $35.30  
  Purchase #3 $122.72   3.751%   $127.3232   $127.32   $127.30   $127.30  
  Purchase #4 $217.41   4.377%   $226.926   $226.93   $226.95   $226.90  
  Purchase #5 $115.47   8.524%   $125.3127   $125.31   $125.30   $125.30  
  Purchase #6 $177.29   12.762%   $199.9157   $199.92   $199.90   $199.90  
  Purchase #7 $44.54   7.224%   $47.7576   $47.76   $47.75   $47.80  
  7 purchase totals = $871.41       $945.3207   $945.33   $945.30   $945.20