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 $226.84   12.370%   $254.9001   $254.90   $254.90   $254.90  
  Purchase #2 $27.26   11.704%   $30.4505   $30.45   $30.45   $30.50  
  Purchase #3 $55.77   10.216%   $61.4675   $61.47   $61.45   $61.50  
  Purchase #4 $72.96   13.383%   $82.7242   $82.72   $82.70   $82.70  
  Purchase #5 $49.68   13.137%   $56.2065   $56.21   $56.20   $56.20  
  Purchase #6 $45.46   5.828%   $48.1094   $48.11   $48.10   $48.10  
  Purchase #7 $75.89   5.742%   $80.2476   $80.25   $80.25   $80.20  
  7 purchase totals = $553.86       $614.1058   $614.11   $614.05   $614.10