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 $168.86   10.567%   $186.7034   $186.70   $186.70   $186.70  
  Purchase #2 $93.91   8.244%   $101.6519   $101.65   $101.65   $101.70  
  Purchase #3 $61.69   12.284%   $69.268   $69.27   $69.25   $69.30  
  Purchase #4 $137.32   3.535%   $142.1743   $142.17   $142.15   $142.20  
  Purchase #5 $190.38   7.214%   $204.114   $204.11   $204.10   $204.10  
  Purchase #6 $183.54   12.634%   $206.7284   $206.73   $206.75   $206.70  
  Purchase #7 $108.55   7.852%   $117.0733   $117.07   $117.05   $117.10  
  7 purchase totals = $944.25       $1,027.7133   $1,027.70   $1,027.65   $1,027.80