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 $119.32   3.754%   $123.7993   $123.80   $123.80   $123.80  
  Purchase #2 $227.54   11.187%   $252.9949   $252.99   $253.00   $253.00  
  Purchase #3 $132.75   7.445%   $142.6332   $142.63   $142.65   $142.60  
  Purchase #4 $168.94   4.175%   $175.9932   $175.99   $176.00   $176.00  
  Purchase #5 $176.65   9.428%   $193.3046   $193.30   $193.30   $193.30  
  Purchase #6 $245.98   6.841%   $262.8075   $262.81   $262.80   $262.80  
  Purchase #7 $65.27   7.381%   $70.0876   $70.09   $70.10   $70.10  
  7 purchase totals = $1,136.45       $1,221.6203   $1,221.61   $1,221.65   $1,221.60