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 $192.62   6.529%   $205.1962   $205.20   $205.20   $205.20  
  Purchase #2 $132.86   11.115%   $147.6274   $147.63   $147.65   $147.60  
  Purchase #3 $50.83   5.160%   $53.4528   $53.45   $53.45   $53.50  
  Purchase #4 $125.59   11.188%   $139.641   $139.64   $139.65   $139.60  
  Purchase #5 $230.88   13.368%   $261.744   $261.74   $261.75   $261.70  
  Purchase #6 $71.76   4.287%   $74.8364   $74.84   $74.85   $74.80  
  Purchase #7 $134.74   3.386%   $139.3023   $139.30   $139.30   $139.30  
  7 purchase totals = $939.28       $1,021.8001   $1,021.80   $1,021.85   $1,021.70