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 $241.82   4.557%   $252.8397   $252.84   $252.85   $252.80  
  Purchase #2 $250.28   7.652%   $269.4314   $269.43   $269.45   $269.40  
  Purchase #3 $164.88   6.552%   $175.6829   $175.68   $175.70   $175.70  
  Purchase #4 $209.61   10.718%   $232.076   $232.08   $232.10   $232.10  
  Purchase #5 $96.67   10.401%   $106.7246   $106.72   $106.70   $106.70  
  Purchase #6 $207.48   4.826%   $217.493   $217.49   $217.50   $217.50  
  Purchase #7 $22.51   8.269%   $24.3714   $24.37   $24.35   $24.40  
  7 purchase totals = $1,193.25       $1,278.6190   $1,278.61   $1,278.65   $1,278.60