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 $71.57   4.696%   $74.9309   $74.93   $74.95   $74.90  
  Purchase #2 $195.60   13.832%   $222.6554   $222.66   $222.65   $222.70  
  Purchase #3 $143.86   6.619%   $153.3821   $153.38   $153.40   $153.40  
  Purchase #4 $221.72   9.188%   $242.0916   $242.09   $242.10   $242.10  
  Purchase #5 $146.39   4.483%   $152.9527   $152.95   $152.95   $153.00  
  Purchase #6 $150.44   4.542%   $157.273   $157.27   $157.25   $157.30  
  Purchase #7 $53.36   3.572%   $55.266   $55.27   $55.25   $55.30  
  7 purchase totals = $982.94       $1,058.5517   $1,058.55   $1,058.55   $1,058.70