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 $192.57   6.580%   $205.2411   $205.24   $205.25   $205.20  
  Purchase #2 $9.82   7.864%   $10.5922   $10.59   $10.60   $10.60  
  Purchase #3 $50.80   9.747%   $55.7515   $55.75   $55.75   $55.80  
  Purchase #4 $105.89   10.772%   $117.2965   $117.30   $117.30   $117.30  
  Purchase #5 $70.68   4.488%   $73.8521   $73.85   $73.85   $73.90  
  Purchase #6 $150.82   6.785%   $161.0531   $161.05   $161.05   $161.10  
  Purchase #7 $30.71   4.688%   $32.1497   $32.15   $32.15   $32.10  
  7 purchase totals = $611.29       $655.9362   $655.93   $655.95   $656.00