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 $59.89   11.863%   $66.9948   $66.99   $67.00   $67.00  
  Purchase #2 $86.33   11.411%   $96.1811   $96.18   $96.20   $96.20  
  Purchase #3 $237.45   3.220%   $245.0959   $245.10   $245.10   $245.10  
  Purchase #4 $63.94   6.836%   $68.3109   $68.31   $68.30   $68.30  
  Purchase #5 $23.33   13.834%   $26.5575   $26.56   $26.55   $26.60  
  Purchase #6 $42.57   10.518%   $47.0475   $47.05   $47.05   $47.00  
  Purchase #7 $208.53   4.561%   $218.0411   $218.04   $218.05   $218.00  
  7 purchase totals = $722.04       $768.2288   $768.23   $768.25   $768.20