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 $88.60   3.211%   $91.4449   $91.44   $91.45   $91.40  
  Purchase #2 $193.28   8.118%   $208.9705   $208.97   $208.95   $209.00  
  Purchase #3 $184.65   9.856%   $202.8491   $202.85   $202.85   $202.80  
  Purchase #4 $227.99   10.642%   $252.2527   $252.25   $252.25   $252.30  
  Purchase #5 $62.84   12.260%   $70.5442   $70.54   $70.55   $70.50  
  Purchase #6 $186.40   7.500%   $200.38   $200.38   $200.40   $200.40  
  Purchase #7 $17.69   5.260%   $18.6205   $18.62   $18.60   $18.60  
  7 purchase totals = $961.45       $1,045.0619   $1,045.05   $1,045.05   $1,045.00