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 $91.34   5.711%   $96.5564   $96.56   $96.55   $96.60  
  Purchase #2 $158.39   8.866%   $172.4329   $172.43   $172.45   $172.40  
  Purchase #3 $75.37   3.372%   $77.9115   $77.91   $77.90   $77.90  
  Purchase #4 $181.49   3.368%   $187.6026   $187.60   $187.60   $187.60  
  Purchase #5 $211.30   6.804%   $225.6769   $225.68   $225.70   $225.70  
  Purchase #6 $112.85   8.714%   $122.6837   $122.68   $122.70   $122.70  
  Purchase #7 $124.91   13.271%   $141.4868   $141.49   $141.50   $141.50  
  7 purchase totals = $955.65       $1,024.3508   $1,024.35   $1,024.40   $1,024.40