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 $34.84   4.853%   $36.5308   $36.53   $36.55   $36.50  
  Purchase #2 $156.89   13.415%   $177.9368   $177.94   $177.95   $177.90  
  Purchase #3 $132.94   3.249%   $137.2592   $137.26   $137.25   $137.30  
  Purchase #4 $92.70   4.791%   $97.1413   $97.14   $97.15   $97.10  
  Purchase #5 $76.84   7.719%   $82.7713   $82.77   $82.75   $82.80  
  Purchase #6 $189.43   10.194%   $208.7405   $208.74   $208.75   $208.70  
  Purchase #7 $235.74   8.159%   $254.974   $254.97   $254.95   $255.00  
  7 purchase totals = $919.38       $995.3539   $995.35   $995.35   $995.30