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 $115.95   7.779%   $124.9698   $124.97   $124.95   $125.00  
  Purchase #2 $191.32   6.329%   $203.4286   $203.43   $203.45   $203.40  
  Purchase #3 $176.46   5.552%   $186.2571   $186.26   $186.25   $186.30  
  Purchase #4 $31.59   9.739%   $34.6666   $34.67   $34.65   $34.70  
  Purchase #5 $230.41   12.866%   $260.0546   $260.05   $260.05   $260.10  
  Purchase #6 $47.32   4.476%   $49.438   $49.44   $49.45   $49.40  
  Purchase #7 $244.67   6.433%   $260.4096   $260.41   $260.40   $260.40  
  7 purchase totals = $1,037.72       $1,119.2243   $1,119.23   $1,119.20   $1,119.30