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 $68.91   3.656%   $71.4293   $71.43   $71.45   $71.40  
  Purchase #2 $78.42   7.104%   $83.991   $83.99   $84.00   $84.00  
  Purchase #3 $10.37   12.116%   $11.6264   $11.63   $11.65   $11.60  
  Purchase #4 $144.76   11.672%   $161.6564   $161.66   $161.65   $161.70  
  Purchase #5 $102.34   6.674%   $109.1702   $109.17   $109.15   $109.20  
  Purchase #6 $141.67   6.586%   $151.0004   $151.00   $151.00   $151.00  
  Purchase #7 $250.31   6.687%   $267.0482   $267.05   $267.05   $267.00  
  7 purchase totals = $796.78       $855.9219   $855.93   $855.95   $855.90