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 $142.32   13.847%   $162.0271   $162.03   $162.05   $162.00  
  Purchase #2 $194.27   8.789%   $211.3444   $211.34   $211.35   $211.30  
  Purchase #3 $202.76   11.458%   $225.9922   $225.99   $226.00   $226.00  
  Purchase #4 $34.35   4.737%   $35.9772   $35.98   $36.00   $36.00  
  Purchase #5 $197.83   11.802%   $221.1779   $221.18   $221.20   $221.20  
  Purchase #6 $245.61   4.820%   $257.4484   $257.45   $257.45   $257.40  
  Purchase #7 $118.41   5.705%   $125.1653   $125.17   $125.15   $125.20  
  7 purchase totals = $1,135.55       $1,239.1325   $1,239.14   $1,239.20   $1,239.10