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 $57.65   7.119%   $61.7541   $61.75   $61.75   $61.80  
  Purchase #2 $124.72   13.808%   $141.9413   $141.94   $141.95   $141.90  
  Purchase #3 $50.98   3.678%   $52.855   $52.86   $52.85   $52.90  
  Purchase #4 $164.73   5.420%   $173.6584   $173.66   $173.65   $173.70  
  Purchase #5 $55.99   12.646%   $63.0705   $63.07   $63.05   $63.10  
  Purchase #6 $49.79   12.200%   $55.8644   $55.86   $55.85   $55.90  
  Purchase #7 $15.44   11.761%   $17.2559   $17.26   $17.25   $17.30  
  7 purchase totals = $519.30       $566.3996   $566.40   $566.35   $566.60