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 $137.78   11.563%   $153.7115   $153.71   $153.70   $153.70  
  Purchase #2 $237.77   8.487%   $257.9495   $257.95   $257.95   $257.90  
  Purchase #3 $220.82   8.141%   $238.797   $238.80   $238.80   $238.80  
  Purchase #4 $183.32   13.119%   $207.3698   $207.37   $207.35   $207.40  
  Purchase #5 $111.80   9.734%   $122.6826   $122.68   $122.70   $122.70  
  Purchase #6 $125.44   10.215%   $138.2537   $138.25   $138.25   $138.30  
  Purchase #7 $62.32   7.670%   $67.0999   $67.10   $67.10   $67.10  
  7 purchase totals = $1,079.25       $1,185.8640   $1,185.86   $1,185.85   $1,185.90