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 $232.58   9.158%   $253.8797   $253.88   $253.90   $253.90  
  Purchase #2 $126.95   9.851%   $139.4558   $139.46   $139.45   $139.50  
  Purchase #3 $15.25   5.316%   $16.0607   $16.06   $16.05   $16.10  
  Purchase #4 $222.69   5.571%   $235.0961   $235.10   $235.10   $235.10  
  Purchase #5 $173.31   9.383%   $189.5717   $189.57   $189.55   $189.60  
  Purchase #6 $155.28   4.874%   $162.8483   $162.85   $162.85   $162.80  
  Purchase #7 $49.27   8.708%   $53.5604   $53.56   $53.55   $53.60  
  7 purchase totals = $975.33       $1,050.4727   $1,050.48   $1,050.45   $1,050.60