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 $84.62   11.190%   $94.089   $94.09   $94.10   $94.10  
  Purchase #2 $249.44   13.388%   $282.835   $282.84   $282.85   $282.80  
  Purchase #3 $189.26   10.761%   $209.6263   $209.63   $209.65   $209.60  
  Purchase #4 $228.48   10.578%   $252.6486   $252.65   $252.65   $252.60  
  Purchase #5 $215.61   5.500%   $227.4686   $227.47   $227.45   $227.50  
  Purchase #6 $24.56   9.502%   $26.8937   $26.89   $26.90   $26.90  
  Purchase #7 $30.38   13.302%   $34.4211   $34.42   $34.40   $34.40  
  7 purchase totals = $1,022.35       $1,127.9823   $1,127.99   $1,128.00   $1,127.90