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 $62.62   11.831%   $70.0286   $70.03   $70.05   $70.00  
  Purchase #2 $241.78   4.791%   $253.3637   $253.36   $253.35   $253.40  
  Purchase #3 $126.49   3.560%   $130.993   $130.99   $131.00   $131.00  
  Purchase #4 $157.53   3.571%   $163.1554   $163.16   $163.15   $163.20  
  Purchase #5 $93.51   13.629%   $106.2545   $106.25   $106.25   $106.30  
  Purchase #6 $164.70   13.256%   $186.5326   $186.53   $186.55   $186.50  
  Purchase #7 $86.85   4.219%   $90.5142   $90.51   $90.50   $90.50  
  7 purchase totals = $933.48       $1,000.8420   $1,000.83   $1,000.85   $1,000.90