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 $208.84   12.556%   $235.062   $235.06   $235.05   $235.10  
  Purchase #2 $146.68   10.272%   $161.747   $161.75   $161.75   $161.70  
  Purchase #3 $90.50   5.252%   $95.2531   $95.25   $95.25   $95.30  
  Purchase #4 $184.55   9.629%   $202.3203   $202.32   $202.30   $202.30  
  Purchase #5 $221.28   6.405%   $235.453   $235.45   $235.45   $235.50  
  Purchase #6 $238.56   8.204%   $258.1315   $258.13   $258.15   $258.10  
  Purchase #7 $168.62   8.238%   $182.5109   $182.51   $182.50   $182.50  
  7 purchase totals = $1,259.03       $1,370.4778   $1,370.47   $1,370.45   $1,370.50