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 $71.26   7.841%   $76.8475   $76.85   $76.85   $76.80  
  Purchase #2 $30.89   10.701%   $34.1955   $34.20   $34.20   $34.20  
  Purchase #3 $240.58   10.361%   $265.5065   $265.51   $265.50   $265.50  
  Purchase #4 $8.70   8.812%   $9.4666   $9.47   $9.45   $9.50  
  Purchase #5 $206.73   11.289%   $230.0677   $230.07   $230.05   $230.10  
  Purchase #6 $165.60   4.830%   $173.5985   $173.60   $173.60   $173.60  
  Purchase #7 $240.76   12.236%   $270.2194   $270.22   $270.20   $270.20  
  7 purchase totals = $964.52       $1,059.9017   $1,059.92   $1,059.85   $1,059.90