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 $239.28   8.256%   $259.035   $259.04   $259.05   $259.00  
  Purchase #2 $65.79   7.157%   $70.4986   $70.50   $70.50   $70.50  
  Purchase #3 $34.73   11.313%   $38.659   $38.66   $38.65   $38.70  
  Purchase #4 $65.91   6.614%   $70.2693   $70.27   $70.25   $70.30  
  Purchase #5 $126.86   10.120%   $139.6982   $139.70   $139.70   $139.70  
  Purchase #6 $215.71   8.784%   $234.658   $234.66   $234.65   $234.70  
  Purchase #7 $212.58   7.381%   $228.2705   $228.27   $228.25   $228.30  
  7 purchase totals = $960.86       $1,041.0886   $1,041.10   $1,041.05   $1,041.20