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 $249.43   8.497%   $270.6241   $270.62   $270.60   $270.60  
  Purchase #2 $39.67   6.503%   $42.2497   $42.25   $42.25   $42.20  
  Purchase #3 $207.99   12.672%   $234.3465   $234.35   $234.35   $234.30  
  Purchase #4 $54.83   4.433%   $57.2606   $57.26   $57.25   $57.30  
  Purchase #5 $236.40   9.836%   $259.6523   $259.65   $259.65   $259.70  
  Purchase #6 $49.89   9.449%   $54.6041   $54.60   $54.60   $54.60  
  Purchase #7 $176.55   5.731%   $186.6681   $186.67   $186.65   $186.70  
  7 purchase totals = $1,014.76       $1,105.4054   $1,105.40   $1,105.35   $1,105.40