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 $232.46   3.669%   $240.989   $240.99   $241.00   $241.00  
  Purchase #2 $98.56   5.235%   $103.7196   $103.72   $103.70   $103.70  
  Purchase #3 $80.27   6.199%   $85.2459   $85.25   $85.25   $85.20  
  Purchase #4 $117.36   3.534%   $121.5075   $121.51   $121.50   $121.50  
  Purchase #5 $209.48   8.169%   $226.5924   $226.59   $226.60   $226.60  
  Purchase #6 $99.34   7.105%   $106.3981   $106.40   $106.40   $106.40  
  Purchase #7 $148.53   11.397%   $165.458   $165.46   $165.45   $165.50  
  7 purchase totals = $986.00       $1,049.9105   $1,049.92   $1,049.90   $1,049.90