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 $184.97   12.779%   $208.6073   $208.61   $208.60   $208.60  
  Purchase #2 $46.50   6.634%   $49.5848   $49.58   $49.60   $49.60  
  Purchase #3 $55.37   5.196%   $58.247   $58.25   $58.25   $58.20  
  Purchase #4 $188.84   10.693%   $209.0327   $209.03   $209.05   $209.00  
  Purchase #5 $75.61   13.219%   $85.6049   $85.60   $85.60   $85.60  
  Purchase #6 $247.58   9.253%   $270.4886   $270.49   $270.50   $270.50  
  Purchase #7 $237.34   9.539%   $259.9799   $259.98   $260.00   $260.00  
  7 purchase totals = $1,036.21       $1,141.5452   $1,141.54   $1,141.60   $1,141.50