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 $250.74   10.266%   $276.481   $276.48   $276.50   $276.50  
  Purchase #2 $58.48   7.647%   $62.952   $62.95   $62.95   $63.00  
  Purchase #3 $187.45   4.275%   $195.4635   $195.46   $195.45   $195.50  
  Purchase #4 $95.68   5.124%   $100.5826   $100.58   $100.60   $100.60  
  Purchase #5 $87.64   12.265%   $98.389   $98.39   $98.40   $98.40  
  Purchase #6 $121.70   11.520%   $135.7198   $135.72   $135.70   $135.70  
  Purchase #7 $227.67   12.718%   $256.6251   $256.63   $256.65   $256.60  
  7 purchase totals = $1,029.36       $1,126.2130   $1,126.21   $1,126.25   $1,126.30