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 $224.41   13.615%   $254.9634   $254.96   $254.95   $255.00  
  Purchase #2 $23.86   12.598%   $26.8659   $26.87   $26.85   $26.90  
  Purchase #3 $214.39   13.408%   $243.1354   $243.14   $243.15   $243.10  
  Purchase #4 $149.49   4.455%   $156.1498   $156.15   $156.15   $156.10  
  Purchase #5 $97.99   11.146%   $108.912   $108.91   $108.90   $108.90  
  Purchase #6 $10.26   13.337%   $11.6284   $11.63   $11.65   $11.60  
  Purchase #7 $32.97   5.538%   $34.7959   $34.80   $34.80   $34.80  
  7 purchase totals = $753.37       $836.4508   $836.46   $836.45   $836.40