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 $7.42   8.866%   $8.0779   $8.08   $8.10   $8.10  
  Purchase #2 $109.94   5.324%   $115.7932   $115.79   $115.80   $115.80  
  Purchase #3 $46.73   3.269%   $48.2576   $48.26   $48.25   $48.30  
  Purchase #4 $87.39   3.599%   $90.5352   $90.54   $90.55   $90.50  
  Purchase #5 $139.87   11.193%   $155.5256   $155.53   $155.55   $155.50  
  Purchase #6 $10.44   4.498%   $10.9096   $10.91   $10.90   $10.90  
  Purchase #7 $73.79   9.659%   $80.9174   $80.92   $80.90   $80.90  
  7 purchase totals = $475.58       $510.0165   $510.03   $510.05   $510.00