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 $98.45   5.845%   $104.2044   $104.20   $104.20   $104.20  
  Purchase #2 $194.50   6.617%   $207.3701   $207.37   $207.35   $207.40  
  Purchase #3 $242.80   6.252%   $257.9799   $257.98   $258.00   $258.00  
  Purchase #4 $74.52   6.102%   $79.0672   $79.07   $79.05   $79.10  
  Purchase #5 $176.27   11.604%   $196.7244   $196.72   $196.70   $196.70  
  Purchase #6 $136.98   10.690%   $151.6232   $151.62   $151.60   $151.60  
  Purchase #7 $49.33   8.484%   $53.5152   $53.52   $53.50   $53.50  
  7 purchase totals = $972.85       $1,050.4844   $1,050.48   $1,050.40   $1,050.50