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 $205.93   5.230%   $216.7001   $216.70   $216.70   $216.70  
  Purchase #2 $112.59   7.804%   $121.3765   $121.38   $121.40   $121.40  
  Purchase #3 $64.38   5.462%   $67.8964   $67.90   $67.90   $67.90  
  Purchase #4 $244.51   7.850%   $263.704   $263.70   $263.70   $263.70  
  Purchase #5 $23.76   8.855%   $25.8639   $25.86   $25.85   $25.90  
  Purchase #6 $35.35   13.771%   $40.218   $40.22   $40.20   $40.20  
  Purchase #7 $36.42   10.482%   $40.2375   $40.24   $40.25   $40.20  
  7 purchase totals = $722.94       $775.9964   $776.00   $776.00   $776.00