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 $74.62   13.249%   $84.5064   $84.51   $84.50   $84.50  
  Purchase #2 $191.27   7.302%   $205.2365   $205.24   $205.25   $205.20  
  Purchase #3 $176.99   8.712%   $192.4094   $192.41   $192.40   $192.40  
  Purchase #4 $52.46   4.242%   $54.6854   $54.69   $54.70   $54.70  
  Purchase #5 $87.77   9.396%   $96.0169   $96.02   $96.00   $96.00  
  Purchase #6 $53.81   4.786%   $56.3853   $56.39   $56.40   $56.40  
  Purchase #7 $14.44   8.715%   $15.6984   $15.70   $15.70   $15.70  
  7 purchase totals = $651.36       $704.9383   $704.96   $704.95   $704.90