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 $44.32   4.493%   $46.3113   $46.31   $46.30   $46.30  
  Purchase #2 $95.40   8.837%   $103.8305   $103.83   $103.85   $103.80  
  Purchase #3 $189.64   6.258%   $201.5077   $201.51   $201.50   $201.50  
  Purchase #4 $52.88   8.445%   $57.3457   $57.35   $57.35   $57.30  
  Purchase #5 $13.74   4.134%   $14.308   $14.31   $14.30   $14.30  
  Purchase #6 $51.55   3.273%   $53.2372   $53.24   $53.25   $53.20  
  Purchase #7 $16.29   4.716%   $17.0582   $17.06   $17.05   $17.10  
  7 purchase totals = $463.82       $493.5986   $493.61   $493.60   $493.50