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 $207.30   12.376%   $232.9554   $232.96   $232.95   $233.00  
  Purchase #2 $101.66   7.828%   $109.6179   $109.62   $109.60   $109.60  
  Purchase #3 $173.87   7.422%   $186.7746   $186.77   $186.75   $186.80  
  Purchase #4 $90.68   11.724%   $101.3113   $101.31   $101.30   $101.30  
  Purchase #5 $172.33   13.863%   $196.2201   $196.22   $196.20   $196.20  
  Purchase #6 $23.94   8.601%   $25.9991   $26.00   $26.00   $26.00  
  Purchase #7 $113.59   8.275%   $122.9896   $122.99   $123.00   $123.00  
  7 purchase totals = $883.37       $975.8680   $975.87   $975.80   $975.90