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 $55.88   11.577%   $62.3492   $62.35   $62.35   $62.30  
  Purchase #2 $149.99   4.614%   $156.9105   $156.91   $156.90   $156.90  
  Purchase #3 $247.64   10.299%   $273.1444   $273.14   $273.15   $273.10  
  Purchase #4 $38.32   3.712%   $39.7424   $39.74   $39.75   $39.70  
  Purchase #5 $34.35   13.387%   $38.9484   $38.95   $38.95   $38.90  
  Purchase #6 $162.84   12.602%   $183.3611   $183.36   $183.35   $183.40  
  Purchase #7 $202.29   9.623%   $221.7564   $221.76   $221.75   $221.80  
  7 purchase totals = $891.31       $976.2124   $976.21   $976.20   $976.10