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 $246.99   11.155%   $274.5417   $274.54   $274.55   $274.50  
  Purchase #2 $33.63   11.314%   $37.4349   $37.43   $37.45   $37.40  
  Purchase #3 $235.41   5.722%   $248.8802   $248.88   $248.90   $248.90  
  Purchase #4 $112.82   3.369%   $116.6209   $116.62   $116.60   $116.60  
  Purchase #5 $68.88   6.296%   $73.2167   $73.22   $73.20   $73.20  
  Purchase #6 $204.94   9.734%   $224.8889   $224.89   $224.90   $224.90  
  Purchase #7 $81.40   4.381%   $84.9661   $84.97   $84.95   $85.00  
  7 purchase totals = $984.07       $1,060.5494   $1,060.55   $1,060.55   $1,060.50