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 $171.37   13.392%   $194.3199   $194.32   $194.30   $194.30  
  Purchase #2 $216.46   10.838%   $239.9199   $239.92   $239.90   $239.90  
  Purchase #3 $116.87   5.656%   $123.4802   $123.48   $123.50   $123.50  
  Purchase #4 $62.41   3.380%   $64.5195   $64.52   $64.50   $64.50  
  Purchase #5 $119.61   11.652%   $133.547   $133.55   $133.55   $133.50  
  Purchase #6 $158.49   9.335%   $173.285   $173.29   $173.30   $173.30  
  Purchase #7 $113.88   10.832%   $126.2155   $126.22   $126.20   $126.20  
  7 purchase totals = $959.09       $1,055.2870   $1,055.30   $1,055.25   $1,055.20