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 $225.88   7.258%   $242.2744   $242.27   $242.25   $242.30  
  Purchase #2 $181.44   6.551%   $193.3261   $193.33   $193.35   $193.30  
  Purchase #3 $171.33   12.446%   $192.6537   $192.65   $192.65   $192.70  
  Purchase #4 $24.25   4.659%   $25.3798   $25.38   $25.40   $25.40  
  Purchase #5 $156.59   10.595%   $173.1807   $173.18   $173.20   $173.20  
  Purchase #6 $73.53   4.253%   $76.6572   $76.66   $76.65   $76.70  
  Purchase #7 $54.30   5.204%   $57.1258   $57.13   $57.15   $57.10  
  7 purchase totals = $887.32       $960.5977   $960.60   $960.65   $960.70