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 $73.66   3.592%   $76.3059   $76.31   $76.30   $76.30  
  Purchase #2 $129.54   13.719%   $147.3116   $147.31   $147.30   $147.30  
  Purchase #3 $122.38   13.281%   $138.6333   $138.63   $138.65   $138.60  
  Purchase #4 $152.84   12.854%   $172.4861   $172.49   $172.50   $172.50  
  Purchase #5 $161.39   9.127%   $176.1201   $176.12   $176.10   $176.10  
  Purchase #6 $90.77   5.379%   $95.6525   $95.65   $95.65   $95.70  
  Purchase #7 $188.28   6.122%   $199.8065   $199.81   $199.80   $199.80  
  7 purchase totals = $918.86       $1,006.3160   $1,006.32   $1,006.30   $1,006.30