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 $232.30   12.420%   $261.1517   $261.15   $261.15   $261.20  
  Purchase #2 $212.70   5.613%   $224.6389   $224.64   $224.65   $224.60  
  Purchase #3 $187.82   13.856%   $213.8443   $213.84   $213.85   $213.80  
  Purchase #4 $114.47   8.162%   $123.813   $123.81   $123.80   $123.80  
  Purchase #5 $86.71   9.575%   $95.0125   $95.01   $95.00   $95.00  
  Purchase #6 $205.57   3.477%   $212.7177   $212.72   $212.70   $212.70  
  Purchase #7 $153.32   11.207%   $170.5026   $170.50   $170.50   $170.50  
  7 purchase totals = $1,192.89       $1,301.6807   $1,301.67   $1,301.65   $1,301.60