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 $199.58   7.632%   $214.8119   $214.81   $214.80   $214.80  
  Purchase #2 $24.55   10.735%   $27.1854   $27.19   $27.20   $27.20  
  Purchase #3 $104.27   11.126%   $115.8711   $115.87   $115.85   $115.90  
  Purchase #4 $167.87   8.463%   $182.0768   $182.08   $182.10   $182.10  
  Purchase #5 $174.95   6.738%   $186.7381   $186.74   $186.75   $186.70  
  Purchase #6 $156.53   6.429%   $166.5933   $166.59   $166.60   $166.60  
  Purchase #7 $112.52   12.583%   $126.6784   $126.68   $126.70   $126.70  
  7 purchase totals = $940.27       $1,019.9550   $1,019.96   $1,020.00   $1,020.00