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 $186.81   13.246%   $211.5549   $211.55   $211.55   $211.60  
  Purchase #2 $197.44   3.827%   $204.996   $205.00   $205.00   $205.00  
  Purchase #3 $157.35   11.638%   $175.6624   $175.66   $175.65   $175.70  
  Purchase #4 $240.78   12.687%   $271.3278   $271.33   $271.35   $271.30  
  Purchase #5 $42.95   9.365%   $46.9723   $46.97   $46.95   $47.00  
  Purchase #6 $9.48   3.202%   $9.7835   $9.78   $9.80   $9.80  
  Purchase #7 $87.25   10.144%   $96.1006   $96.10   $96.10   $96.10  
  7 purchase totals = $922.06       $1,016.3975   $1,016.39   $1,016.40   $1,016.50