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 $193.49   8.324%   $209.5961   $209.60   $209.60   $209.60  
  Purchase #2 $6.71   3.381%   $6.9369   $6.94   $6.95   $6.90  
  Purchase #3 $53.90   7.180%   $57.77   $57.77   $57.75   $57.80  
  Purchase #4 $228.50   10.236%   $251.8893   $251.89   $251.90   $251.90  
  Purchase #5 $30.85   6.107%   $32.734   $32.73   $32.75   $32.70  
  Purchase #6 $210.56   10.851%   $233.4079   $233.41   $233.40   $233.40  
  Purchase #7 $172.66   13.692%   $196.3006   $196.30   $196.30   $196.30  
  7 purchase totals = $896.67       $988.6348   $988.64   $988.65   $988.60