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 $35.52   8.786%   $38.6408   $38.64   $38.65   $38.60  
  Purchase #2 $90.85   10.114%   $100.0386   $100.04   $100.05   $100.00  
  Purchase #3 $204.80   6.566%   $218.2472   $218.25   $218.25   $218.20  
  Purchase #4 $207.64   13.493%   $235.6569   $235.66   $235.65   $235.70  
  Purchase #5 $69.89   9.276%   $76.373   $76.37   $76.35   $76.40  
  Purchase #6 $239.95   8.193%   $259.6091   $259.61   $259.60   $259.60  
  Purchase #7 $88.62   8.274%   $95.9524   $95.95   $95.95   $96.00  
  7 purchase totals = $937.27       $1,024.5180   $1,024.52   $1,024.50   $1,024.50