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 $214.78   8.254%   $232.5079   $232.51   $232.50   $232.50  
  Purchase #2 $151.57   11.438%   $168.9066   $168.91   $168.90   $168.90  
  Purchase #3 $238.75   12.546%   $268.7036   $268.70   $268.70   $268.70  
  Purchase #4 $212.86   4.198%   $221.7959   $221.80   $221.80   $221.80  
  Purchase #5 $11.25   9.626%   $12.3329   $12.33   $12.35   $12.30  
  Purchase #6 $228.38   5.711%   $241.4228   $241.42   $241.40   $241.40  
  Purchase #7 $179.64   3.223%   $185.4298   $185.43   $185.45   $185.40  
  7 purchase totals = $1,237.23       $1,331.0995   $1,331.10   $1,331.10   $1,331.00