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 $167.79   4.453%   $175.2617   $175.26   $175.25   $175.30  
  Purchase #2 $175.90   8.794%   $191.3686   $191.37   $191.35   $191.40  
  Purchase #3 $60.57   13.538%   $68.77   $68.77   $68.75   $68.80  
  Purchase #4 $162.62   10.481%   $179.6642   $179.66   $179.65   $179.70  
  Purchase #5 $94.65   12.564%   $106.5418   $106.54   $106.55   $106.50  
  Purchase #6 $46.34   4.823%   $48.575   $48.58   $48.60   $48.60  
  Purchase #7 $174.45   13.672%   $198.3008   $198.30   $198.30   $198.30  
  7 purchase totals = $882.32       $968.4821   $968.48   $968.45   $968.60