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 $240.73   3.329%   $248.7439   $248.74   $248.75   $248.70  
  Purchase #2 $60.66   11.426%   $67.591   $67.59   $67.60   $67.60  
  Purchase #3 $5.95   4.753%   $6.2328   $6.23   $6.25   $6.20  
  Purchase #4 $24.45   8.755%   $26.5906   $26.59   $26.60   $26.60  
  Purchase #5 $80.66   6.691%   $86.057   $86.06   $86.05   $86.10  
  Purchase #6 $114.76   9.841%   $126.0535   $126.05   $126.05   $126.10  
  Purchase #7 $6.65   4.663%   $6.9601   $6.96   $6.95   $7.00  
  7 purchase totals = $533.86       $568.2289   $568.22   $568.25   $568.30