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 $149.87   10.463%   $165.5509   $165.55   $165.55   $165.60  
  Purchase #2 $235.69   8.138%   $254.8705   $254.87   $254.85   $254.90  
  Purchase #3 $69.33   13.508%   $78.6951   $78.70   $78.70   $78.70  
  Purchase #4 $241.37   12.362%   $271.2082   $271.21   $271.20   $271.20  
  Purchase #5 $99.85   3.189%   $103.0342   $103.03   $103.05   $103.00  
  Purchase #6 $153.25   5.271%   $161.3278   $161.33   $161.35   $161.30  
  Purchase #7 $248.61   8.205%   $269.0085   $269.01   $269.00   $269.00  
  7 purchase totals = $1,197.97       $1,303.6952   $1,303.70   $1,303.70   $1,303.70