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 $226.42   8.624%   $245.9465   $245.95   $245.95   $245.90  
  Purchase #2 $183.57   10.168%   $202.2354   $202.24   $202.25   $202.20  
  Purchase #3 $39.33   11.192%   $43.7318   $43.73   $43.75   $43.70  
  Purchase #4 $10.39   7.245%   $11.1428   $11.14   $11.15   $11.10  
  Purchase #5 $113.52   8.649%   $123.3383   $123.34   $123.35   $123.30  
  Purchase #6 $236.39   13.245%   $267.6999   $267.70   $267.70   $267.70  
  Purchase #7 $5.94   11.544%   $6.6257   $6.63   $6.65   $6.60  
  7 purchase totals = $815.56       $900.7204   $900.73   $900.80   $900.50