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 $23.82   13.221%   $26.9692   $26.97   $26.95   $27.00  
  Purchase #2 $236.48   12.209%   $265.3518   $265.35   $265.35   $265.40  
  Purchase #3 $248.84   5.431%   $262.3545   $262.35   $262.35   $262.40  
  Purchase #4 $50.65   12.399%   $56.9301   $56.93   $56.95   $56.90  
  Purchase #5 $228.83   7.759%   $246.5849   $246.58   $246.60   $246.60  
  Purchase #6 $69.50   6.361%   $73.9209   $73.92   $73.90   $73.90  
  Purchase #7 $126.45   13.337%   $143.3146   $143.31   $143.30   $143.30  
  7 purchase totals = $984.57       $1,075.4260   $1,075.41   $1,075.40   $1,075.50