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 $236.65   13.656%   $268.9669   $268.97   $268.95   $269.00  
  Purchase #2 $137.27   3.107%   $141.535   $141.54   $141.55   $141.50  
  Purchase #3 $172.48   10.749%   $191.0199   $191.02   $191.00   $191.00  
  Purchase #4 $62.98   7.368%   $67.6204   $67.62   $67.60   $67.60  
  Purchase #5 $238.80   9.304%   $261.018   $261.02   $261.00   $261.00  
  Purchase #6 $78.49   5.256%   $82.6154   $82.62   $82.60   $82.60  
  Purchase #7 $49.91   6.411%   $53.1097   $53.11   $53.10   $53.10  
  7 purchase totals = $976.58       $1,065.8853   $1,065.90   $1,065.80   $1,065.80