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 $27.48   8.268%   $29.752   $29.75   $29.75   $29.80  
  Purchase #2 $216.53   5.557%   $228.5626   $228.56   $228.55   $228.60  
  Purchase #3 $102.94   3.651%   $106.6983   $106.70   $106.70   $106.70  
  Purchase #4 $168.26   9.109%   $183.5868   $183.59   $183.60   $183.60  
  Purchase #5 $186.71   11.543%   $208.2619   $208.26   $208.25   $208.30  
  Purchase #6 $51.87   4.704%   $54.31   $54.31   $54.30   $54.30  
  Purchase #7 $29.26   10.579%   $32.3554   $32.36   $32.35   $32.40  
  7 purchase totals = $783.05       $843.5270   $843.53   $843.50   $843.70