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 $56.46   6.509%   $60.135   $60.14   $60.15   $60.10  
  Purchase #2 $58.35   11.233%   $64.9045   $64.90   $64.90   $64.90  
  Purchase #3 $220.36   12.340%   $247.5524   $247.55   $247.55   $247.60  
  Purchase #4 $61.37   8.839%   $66.7945   $66.79   $66.80   $66.80  
  Purchase #5 $6.73   7.773%   $7.2531   $7.25   $7.25   $7.30  
  Purchase #6 $96.88   6.518%   $103.1946   $103.19   $103.20   $103.20  
  Purchase #7 $184.40   4.346%   $192.414   $192.41   $192.40   $192.40  
  7 purchase totals = $684.55       $742.2481   $742.23   $742.25   $742.30