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 $164.60   11.682%   $183.8286   $183.83   $183.85   $183.80  
  Purchase #2 $115.41   9.734%   $126.644   $126.64   $126.65   $126.60  
  Purchase #3 $225.54   12.502%   $253.737   $253.74   $253.75   $253.70  
  Purchase #4 $57.42   9.857%   $63.0799   $63.08   $63.10   $63.10  
  Purchase #5 $206.71   11.527%   $230.5375   $230.54   $230.55   $230.50  
  Purchase #6 $13.51   4.348%   $14.0974   $14.10   $14.10   $14.10  
  Purchase #7 $170.62   7.663%   $183.6946   $183.69   $183.70   $183.70  
  7 purchase totals = $953.81       $1,055.6190   $1,055.62   $1,055.70   $1,055.50