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 $242.87   7.486%   $261.0512   $261.05   $261.05   $261.10  
  Purchase #2 $146.95   5.392%   $154.8735   $154.87   $154.85   $154.90  
  Purchase #3 $87.42   9.240%   $95.4976   $95.50   $95.50   $95.50  
  Purchase #4 $162.43   7.705%   $174.9452   $174.95   $174.95   $174.90  
  Purchase #5 $43.33   6.589%   $46.185   $46.19   $46.20   $46.20  
  Purchase #6 $45.41   5.194%   $47.7686   $47.77   $47.75   $47.80  
  Purchase #7 $73.32   6.860%   $78.3498   $78.35   $78.35   $78.30  
  7 purchase totals = $801.73       $858.6709   $858.68   $858.65   $858.70