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 $106.71   11.255%   $118.7202   $118.72   $118.70   $118.70  
  Purchase #2 $179.42   12.558%   $201.9516   $201.95   $201.95   $202.00  
  Purchase #3 $54.74   12.451%   $61.5557   $61.56   $61.55   $61.60  
  Purchase #4 $36.55   5.664%   $38.6202   $38.62   $38.60   $38.60  
  Purchase #5 $51.27   9.517%   $56.1494   $56.15   $56.15   $56.10  
  Purchase #6 $197.79   12.629%   $222.7689   $222.77   $222.75   $222.80  
  Purchase #7 $32.56   10.565%   $36   $36.00   $36.00   $36.00  
  7 purchase totals = $659.04       $735.7660   $735.77   $735.70   $735.80