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 $80.83   5.832%   $85.544   $85.54   $85.55   $85.50  
  Purchase #2 $221.26   11.299%   $246.2602   $246.26   $246.25   $246.30  
  Purchase #3 $90.44   8.688%   $98.2974   $98.30   $98.30   $98.30  
  Purchase #4 $118.44   4.797%   $124.1216   $124.12   $124.10   $124.10  
  Purchase #5 $213.49   6.591%   $227.5611   $227.56   $227.55   $227.60  
  Purchase #6 $22.82   9.185%   $24.916   $24.92   $24.90   $24.90  
  Purchase #7 $205.48   8.473%   $222.8903   $222.89   $222.90   $222.90  
  7 purchase totals = $952.76       $1,029.5906   $1,029.59   $1,029.55   $1,029.60