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 $234.82   11.578%   $262.0075   $262.01   $262.00   $262.00  
  Purchase #2 $123.43   5.771%   $130.5531   $130.55   $130.55   $130.60  
  Purchase #3 $128.45   4.294%   $133.9656   $133.97   $133.95   $134.00  
  Purchase #4 $188.84   13.299%   $213.9538   $213.95   $213.95   $214.00  
  Purchase #5 $55.46   10.381%   $61.2173   $61.22   $61.20   $61.20  
  Purchase #6 $232.70   12.744%   $262.3553   $262.36   $262.35   $262.40  
  Purchase #7 $112.34   9.657%   $123.1887   $123.19   $123.20   $123.20  
  7 purchase totals = $1,076.04       $1,187.2413   $1,187.25   $1,187.20   $1,187.40