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 $126.79   11.521%   $141.3975   $141.40   $141.40   $141.40  
  Purchase #2 $96.52   5.178%   $101.5178   $101.52   $101.50   $101.50  
  Purchase #3 $113.71   9.176%   $124.144   $124.14   $124.15   $124.10  
  Purchase #4 $202.56   9.520%   $221.8437   $221.84   $221.85   $221.80  
  Purchase #5 $212.63   4.260%   $221.688   $221.69   $221.70   $221.70  
  Purchase #6 $114.49   4.665%   $119.831   $119.83   $119.85   $119.80  
  Purchase #7 $114.92   9.154%   $125.4398   $125.44   $125.45   $125.40  
  7 purchase totals = $981.62       $1,055.8618   $1,055.86   $1,055.90   $1,055.70