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 $167.93   11.217%   $186.7667   $186.77   $186.75   $186.80  
  Purchase #2 $174.43   8.751%   $189.6944   $189.69   $189.70   $189.70  
  Purchase #3 $59.76   4.613%   $62.5167   $62.52   $62.50   $62.50  
  Purchase #4 $10.81   7.354%   $11.605   $11.61   $11.60   $11.60  
  Purchase #5 $189.36   8.153%   $204.7985   $204.80   $204.80   $204.80  
  Purchase #6 $215.86   4.741%   $226.0939   $226.09   $226.10   $226.10  
  Purchase #7 $177.76   11.526%   $198.2486   $198.25   $198.25   $198.20  
  7 purchase totals = $995.91       $1,079.7238   $1,079.73   $1,079.70   $1,079.70