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 $235.41   7.438%   $252.9198   $252.92   $252.90   $252.90  
  Purchase #2 $207.67   6.624%   $221.4261   $221.43   $221.45   $221.40  
  Purchase #3 $111.55   3.401%   $115.3438   $115.34   $115.35   $115.30  
  Purchase #4 $131.55   11.410%   $146.5599   $146.56   $146.55   $146.60  
  Purchase #5 $201.50   6.599%   $214.797   $214.80   $214.80   $214.80  
  Purchase #6 $80.35   5.241%   $84.5611   $84.56   $84.55   $84.60  
  Purchase #7 $222.64   11.114%   $247.3842   $247.38   $247.40   $247.40  
  7 purchase totals = $1,190.67       $1,282.9919   $1,282.99   $1,283.00   $1,283.00