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 $7.38   4.288%   $7.6965   $7.70   $7.70   $7.70  
  Purchase #2 $115.56   7.818%   $124.5945   $124.59   $124.60   $124.60  
  Purchase #3 $243.25   5.863%   $257.5117   $257.51   $257.50   $257.50  
  Purchase #4 $124.33   10.626%   $137.5413   $137.54   $137.55   $137.50  
  Purchase #5 $144.69   9.400%   $158.2909   $158.29   $158.30   $158.30  
  Purchase #6 $18.64   6.331%   $19.8201   $19.82   $19.80   $19.80  
  Purchase #7 $242.84   9.190%   $265.157   $265.16   $265.15   $265.20  
  7 purchase totals = $896.69       $970.6120   $970.61   $970.60   $970.60