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 $240.37   9.786%   $263.8926   $263.89   $263.90   $263.90  
  Purchase #2 $5.83   7.830%   $6.2865   $6.29   $6.30   $6.30  
  Purchase #3 $87.60   6.239%   $93.0654   $93.07   $93.05   $93.10  
  Purchase #4 $208.54   9.343%   $228.0239   $228.02   $228.00   $228.00  
  Purchase #5 $171.86   8.581%   $186.6073   $186.61   $186.60   $186.60  
  Purchase #6 $85.61   11.550%   $95.498   $95.50   $95.50   $95.50  
  Purchase #7 $176.85   9.703%   $194.0098   $194.01   $194.00   $194.00  
  7 purchase totals = $976.66       $1,067.3835   $1,067.39   $1,067.35   $1,067.40