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 $187.60   9.477%   $205.3789   $205.38   $205.40   $205.40  
  Purchase #2 $90.56   13.813%   $103.0691   $103.07   $103.05   $103.10  
  Purchase #3 $74.73   4.863%   $78.3641   $78.36   $78.35   $78.40  
  Purchase #4 $154.36   10.323%   $170.2946   $170.29   $170.30   $170.30  
  Purchase #5 $139.85   9.471%   $153.0952   $153.10   $153.10   $153.10  
  Purchase #6 $11.70   8.826%   $12.7326   $12.73   $12.75   $12.70  
  Purchase #7 $186.56   13.685%   $212.0907   $212.09   $212.10   $212.10  
  7 purchase totals = $845.36       $935.0252   $935.02   $935.05   $935.10