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 $179.73   7.164%   $192.6059   $192.61   $192.60   $192.60  
  Purchase #2 $64.71   13.430%   $73.4006   $73.40   $73.40   $73.40  
  Purchase #3 $69.26   5.603%   $73.1406   $73.14   $73.15   $73.10  
  Purchase #4 $235.76   6.348%   $250.726   $250.73   $250.75   $250.70  
  Purchase #5 $226.40   9.237%   $247.3126   $247.31   $247.30   $247.30  
  Purchase #6 $110.43   4.545%   $115.449   $115.45   $115.45   $115.40  
  Purchase #7 $79.82   13.593%   $90.6699   $90.67   $90.65   $90.70  
  7 purchase totals = $966.11       $1,043.3046   $1,043.31   $1,043.30   $1,043.20