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 $33.39   6.416%   $35.5323   $35.53   $35.55   $35.50  
  Purchase #2 $177.66   10.509%   $196.3303   $196.33   $196.35   $196.30  
  Purchase #3 $72.44   10.268%   $79.8781   $79.88   $79.90   $79.90  
  Purchase #4 $200.40   3.146%   $206.7046   $206.70   $206.70   $206.70  
  Purchase #5 $50.36   13.869%   $57.3444   $57.34   $57.35   $57.30  
  Purchase #6 $77.26   6.495%   $82.278   $82.28   $82.30   $82.30  
  Purchase #7 $180.78   9.126%   $197.278   $197.28   $197.30   $197.30  
  7 purchase totals = $792.29       $855.3457   $855.34   $855.45   $855.30