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 $242.80   7.810%   $261.7627   $261.76   $261.75   $261.80  
  Purchase #2 $228.62   11.702%   $255.3731   $255.37   $255.35   $255.40  
  Purchase #3 $80.44   8.581%   $87.3426   $87.34   $87.35   $87.30  
  Purchase #4 $233.55   11.575%   $260.5834   $260.58   $260.60   $260.60  
  Purchase #5 $230.45   3.304%   $238.0641   $238.06   $238.05   $238.10  
  Purchase #6 $56.65   6.242%   $60.1861   $60.19   $60.20   $60.20  
  Purchase #7 $222.59   4.737%   $233.1341   $233.13   $233.15   $233.10  
  7 purchase totals = $1,295.10       $1,396.4461   $1,396.43   $1,396.45   $1,396.50