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 $245.86   3.409%   $254.2414   $254.24   $254.25   $254.20  
  Purchase #2 $188.25   8.221%   $203.726   $203.73   $203.75   $203.70  
  Purchase #3 $166.75   10.399%   $184.0903   $184.09   $184.10   $184.10  
  Purchase #4 $58.25   7.195%   $62.4411   $62.44   $62.45   $62.40  
  Purchase #5 $38.90   12.405%   $43.7255   $43.73   $43.75   $43.70  
  Purchase #6 $221.85   9.425%   $242.7594   $242.76   $242.75   $242.80  
  Purchase #7 $30.79   5.246%   $32.4052   $32.41   $32.40   $32.40  
  7 purchase totals = $950.65       $1,023.3889   $1,023.40   $1,023.45   $1,023.30