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 $161.93   12.689%   $182.4773   $182.48   $182.50   $182.50  
  Purchase #2 $175.55   11.797%   $196.2596   $196.26   $196.25   $196.30  
  Purchase #3 $221.30   6.126%   $234.8568   $234.86   $234.85   $234.90  
  Purchase #4 $44.73   10.693%   $49.513   $49.51   $49.50   $49.50  
  Purchase #5 $124.89   9.603%   $136.8832   $136.88   $136.90   $136.90  
  Purchase #6 $196.64   3.202%   $202.9364   $202.94   $202.95   $202.90  
  Purchase #7 $248.47   6.591%   $264.8467   $264.85   $264.85   $264.80  
  7 purchase totals = $1,173.51       $1,267.7730   $1,267.78   $1,267.80   $1,267.80