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 $114.26   4.133%   $118.9824   $118.98   $119.00   $119.00  
  Purchase #2 $44.52   5.218%   $46.8431   $46.84   $46.85   $46.80  
  Purchase #3 $46.40   4.222%   $48.359   $48.36   $48.35   $48.40  
  Purchase #4 $49.72   13.278%   $56.3218   $56.32   $56.30   $56.30  
  Purchase #5 $23.89   12.609%   $26.9023   $26.90   $26.90   $26.90  
  Purchase #6 $96.49   6.750%   $103.0031   $103.00   $103.00   $103.00  
  Purchase #7 $181.76   10.720%   $201.2447   $201.24   $201.25   $201.20  
  7 purchase totals = $557.04       $601.6564   $601.64   $601.65   $601.60