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 $241.90   11.294%   $269.2202   $269.22   $269.20   $269.20  
  Purchase #2 $229.28   5.746%   $242.4544   $242.45   $242.45   $242.50  
  Purchase #3 $116.94   10.242%   $128.917   $128.92   $128.90   $128.90  
  Purchase #4 $172.65   6.128%   $183.23   $183.23   $183.25   $183.20  
  Purchase #5 $236.87   9.715%   $259.8819   $259.88   $259.90   $259.90  
  Purchase #6 $111.91   3.731%   $116.0854   $116.09   $116.10   $116.10  
  Purchase #7 $67.46   11.346%   $75.114   $75.11   $75.10   $75.10  
  7 purchase totals = $1,177.01       $1,274.9029   $1,274.90   $1,274.90   $1,274.90