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 $162.29   11.351%   $180.7115   $180.71   $180.70   $180.70  
  Purchase #2 $8.97   9.271%   $9.8016   $9.80   $9.80   $9.80  
  Purchase #3 $107.64   6.214%   $114.3287   $114.33   $114.35   $114.30  
  Purchase #4 $65.65   4.320%   $68.4861   $68.49   $68.50   $68.50  
  Purchase #5 $176.96   11.821%   $197.8784   $197.88   $197.90   $197.90  
  Purchase #6 $34.90   10.307%   $38.4971   $38.50   $38.50   $38.50  
  Purchase #7 $247.51   7.634%   $266.4049   $266.40   $266.40   $266.40  
  7 purchase totals = $803.92       $876.1083   $876.11   $876.15   $876.10