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 $56.90   8.360%   $61.6568   $61.66   $61.65   $61.70  
  Purchase #2 $103.78   8.240%   $112.3315   $112.33   $112.35   $112.30  
  Purchase #3 $87.64   12.308%   $98.4267   $98.43   $98.45   $98.40  
  Purchase #4 $68.71   11.731%   $76.7704   $76.77   $76.75   $76.80  
  Purchase #5 $174.25   10.713%   $192.9174   $192.92   $192.90   $192.90  
  Purchase #6 $160.75   6.466%   $171.1441   $171.14   $171.15   $171.10  
  Purchase #7 $57.94   11.213%   $64.4368   $64.44   $64.45   $64.40  
  7 purchase totals = $709.97       $777.6837   $777.69   $777.70   $777.60