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 $211.88   11.665%   $236.5958   $236.60   $236.60   $236.60  
  Purchase #2 $91.89   5.168%   $96.6389   $96.64   $96.65   $96.60  
  Purchase #3 $7.90   13.173%   $8.9407   $8.94   $8.95   $8.90  
  Purchase #4 $245.87   13.308%   $278.5904   $278.59   $278.60   $278.60  
  Purchase #5 $217.61   9.227%   $237.6889   $237.69   $237.70   $237.70  
  Purchase #6 $179.67   12.863%   $202.781   $202.78   $202.80   $202.80  
  Purchase #7 $177.91   5.812%   $188.2501   $188.25   $188.25   $188.30  
  7 purchase totals = $1,132.73       $1,249.4858   $1,249.49   $1,249.55   $1,249.50