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 $71.36   8.692%   $77.5626   $77.56   $77.55   $77.60  
  Purchase #2 $244.61   12.841%   $276.0204   $276.02   $276.00   $276.00  
  Purchase #3 $55.40   11.570%   $61.8098   $61.81   $61.80   $61.80  
  Purchase #4 $47.71   5.349%   $50.262   $50.26   $50.25   $50.30  
  Purchase #5 $206.30   3.527%   $213.5762   $213.58   $213.60   $213.60  
  Purchase #6 $15.97   11.346%   $17.782   $17.78   $17.80   $17.80  
  Purchase #7 $237.88   9.127%   $259.5913   $259.59   $259.60   $259.60  
  7 purchase totals = $879.23       $956.6043   $956.60   $956.60   $956.70