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 $248.33   5.116%   $261.0346   $261.03   $261.05   $261.00  
  Purchase #2 $10.83   7.153%   $11.6047   $11.60   $11.60   $11.60  
  Purchase #3 $91.80   13.162%   $103.8827   $103.88   $103.90   $103.90  
  Purchase #4 $92.50   4.269%   $96.4488   $96.45   $96.45   $96.40  
  Purchase #5 $25.58   6.258%   $27.1808   $27.18   $27.20   $27.20  
  Purchase #6 $212.50   5.616%   $224.434   $224.43   $224.45   $224.40  
  Purchase #7 $23.67   3.163%   $24.4187   $24.42   $24.40   $24.40  
  7 purchase totals = $705.21       $749.0043   $748.99   $749.05   $748.90