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 $82.79   3.254%   $85.484   $85.48   $85.50   $85.50  
  Purchase #2 $182.65   6.762%   $195.0008   $195.00   $195.00   $195.00  
  Purchase #3 $135.67   12.814%   $153.0548   $153.05   $153.05   $153.10  
  Purchase #4 $78.57   13.383%   $89.085   $89.09   $89.10   $89.10  
  Purchase #5 $219.64   5.805%   $232.3901   $232.39   $232.40   $232.40  
  Purchase #6 $214.61   10.176%   $236.4487   $236.45   $236.45   $236.40  
  Purchase #7 $48.98   5.205%   $51.5294   $51.53   $51.55   $51.50  
  7 purchase totals = $962.91       $1,042.9928   $1,042.99   $1,043.05   $1,043.00