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 $179.55   12.673%   $202.3044   $202.30   $202.30   $202.30  
  Purchase #2 $96.26   10.387%   $106.2585   $106.26   $106.25   $106.30  
  Purchase #3 $37.32   8.854%   $40.6243   $40.62   $40.60   $40.60  
  Purchase #4 $64.85   11.741%   $72.464   $72.46   $72.45   $72.50  
  Purchase #5 $210.28   5.721%   $222.3101   $222.31   $222.30   $222.30  
  Purchase #6 $14.57   9.253%   $15.9182   $15.92   $15.90   $15.90  
  Purchase #7 $33.49   3.722%   $34.7365   $34.74   $34.75   $34.70  
  7 purchase totals = $636.32       $694.6160   $694.61   $694.55   $694.60