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 $146.29   8.366%   $158.5286   $158.53   $158.55   $158.50  
  Purchase #2 $53.81   10.159%   $59.2766   $59.28   $59.30   $59.30  
  Purchase #3 $64.25   4.237%   $66.9723   $66.97   $66.95   $67.00  
  Purchase #4 $183.26   12.355%   $205.9018   $205.90   $205.90   $205.90  
  Purchase #5 $82.55   4.633%   $86.3745   $86.37   $86.35   $86.40  
  Purchase #6 $250.35   13.186%   $283.3612   $283.36   $283.35   $283.40  
  Purchase #7 $84.85   9.335%   $92.7707   $92.77   $92.75   $92.80  
  7 purchase totals = $865.36       $953.1857   $953.18   $953.15   $953.30