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 $59.81   6.446%   $63.6654   $63.67   $63.65   $63.70  
  Purchase #2 $110.67   9.266%   $120.9247   $120.92   $120.90   $120.90  
  Purchase #3 $55.36   13.874%   $63.0406   $63.04   $63.05   $63.00  
  Purchase #4 $178.93   13.823%   $203.6635   $203.66   $203.65   $203.70  
  Purchase #5 $237.74   4.402%   $248.2053   $248.21   $248.20   $248.20  
  Purchase #6 $86.45   7.286%   $92.7487   $92.75   $92.75   $92.70  
  Purchase #7 $66.99   12.688%   $75.4897   $75.49   $75.50   $75.50  
  7 purchase totals = $795.95       $867.7379   $867.74   $867.70   $867.70