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 $127.30   12.103%   $142.7071   $142.71   $142.70   $142.70  
  Purchase #2 $46.44   7.837%   $50.0795   $50.08   $50.10   $50.10  
  Purchase #3 $75.39   4.185%   $78.5451   $78.55   $78.55   $78.50  
  Purchase #4 $13.91   8.495%   $15.0917   $15.09   $15.10   $15.10  
  Purchase #5 $173.36   13.762%   $197.2178   $197.22   $197.20   $197.20  
  Purchase #6 $237.39   4.179%   $247.3105   $247.31   $247.30   $247.30  
  Purchase #7 $90.44   8.536%   $98.16   $98.16   $98.15   $98.20  
  7 purchase totals = $764.23       $829.1117   $829.12   $829.10   $829.10