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 $58.66   4.448%   $61.2692   $61.27   $61.25   $61.30  
  Purchase #2 $53.42   11.490%   $59.558   $59.56   $59.55   $59.60  
  Purchase #3 $177.64   13.542%   $201.696   $201.70   $201.70   $201.70  
  Purchase #4 $99.64   10.608%   $110.2098   $110.21   $110.20   $110.20  
  Purchase #5 $52.45   3.393%   $54.2296   $54.23   $54.25   $54.20  
  Purchase #6 $236.83   3.222%   $244.4607   $244.46   $244.45   $244.50  
  Purchase #7 $244.61   4.135%   $254.7246   $254.72   $254.70   $254.70  
  7 purchase totals = $923.25       $986.1479   $986.15   $986.10   $986.20