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 $175.71   8.539%   $190.7139   $190.71   $190.70   $190.70  
  Purchase #2 $136.95   9.838%   $150.4231   $150.42   $150.40   $150.40  
  Purchase #3 $193.45   9.466%   $211.762   $211.76   $211.75   $211.80  
  Purchase #4 $197.44   8.783%   $214.7812   $214.78   $214.80   $214.80  
  Purchase #5 $61.36   9.751%   $67.3432   $67.34   $67.35   $67.30  
  Purchase #6 $122.39   10.723%   $135.5139   $135.51   $135.50   $135.50  
  Purchase #7 $38.29   13.218%   $43.3512   $43.35   $43.35   $43.40  
  7 purchase totals = $925.59       $1,013.8885   $1,013.87   $1,013.85   $1,013.90