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 $241.49   11.649%   $269.6212   $269.62   $269.60   $269.60  
  Purchase #2 $91.84   7.199%   $98.4516   $98.45   $98.45   $98.50  
  Purchase #3 $236.70   10.349%   $261.1961   $261.20   $261.20   $261.20  
  Purchase #4 $229.84   6.704%   $245.2485   $245.25   $245.25   $245.20  
  Purchase #5 $143.46   13.313%   $162.5588   $162.56   $162.55   $162.60  
  Purchase #6 $52.49   3.576%   $54.367   $54.37   $54.35   $54.40  
  Purchase #7 $11.98   7.371%   $12.863   $12.86   $12.85   $12.90  
  7 purchase totals = $1,007.80       $1,104.3062   $1,104.31   $1,104.25   $1,104.40