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 $61.41   3.712%   $63.6895   $63.69   $63.70   $63.70  
  Purchase #2 $89.80   3.646%   $93.0741   $93.07   $93.05   $93.10  
  Purchase #3 $140.39   11.468%   $156.4899   $156.49   $156.50   $156.50  
  Purchase #4 $231.83   7.365%   $248.9043   $248.90   $248.90   $248.90  
  Purchase #5 $88.88   4.568%   $92.94   $92.94   $92.95   $92.90  
  Purchase #6 $14.26   11.515%   $15.902   $15.90   $15.90   $15.90  
  Purchase #7 $212.54   8.465%   $230.5315   $230.53   $230.55   $230.50  
  7 purchase totals = $839.11       $901.5313   $901.52   $901.55   $901.50