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 $147.78   12.759%   $166.6353   $166.64   $166.65   $166.60  
  Purchase #2 $131.87   3.871%   $136.9747   $136.97   $136.95   $137.00  
  Purchase #3 $44.35   6.735%   $47.337   $47.34   $47.35   $47.30  
  Purchase #4 $208.35   7.727%   $224.4492   $224.45   $224.45   $224.40  
  Purchase #5 $226.59   7.229%   $242.9702   $242.97   $242.95   $243.00  
  Purchase #6 $9.96   12.860%   $11.2409   $11.24   $11.25   $11.20  
  Purchase #7 $115.64   4.691%   $121.0647   $121.06   $121.05   $121.10  
  7 purchase totals = $884.54       $950.6720   $950.67   $950.65   $950.60