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 $128.99   8.329%   $139.7336   $139.73   $139.75   $139.70  
  Purchase #2 $166.47   5.581%   $175.7607   $175.76   $175.75   $175.80  
  Purchase #3 $162.33   3.263%   $167.6268   $167.63   $167.65   $167.60  
  Purchase #4 $46.98   3.401%   $48.5778   $48.58   $48.60   $48.60  
  Purchase #5 $58.28   13.326%   $66.0464   $66.05   $66.05   $66.00  
  Purchase #6 $152.93   6.421%   $162.7496   $162.75   $162.75   $162.70  
  Purchase #7 $235.45   11.748%   $263.1107   $263.11   $263.10   $263.10  
  7 purchase totals = $951.43       $1,023.6056   $1,023.61   $1,023.65   $1,023.50